diff --git a/masque/__init__.py b/masque/__init__.py
index 919a183..bd6908a 100644
--- a/masque/__init__.py
+++ b/masque/__init__.py
@@ -25,7 +25,7 @@
 
 import pathlib
 
-from .error import PatternError
+from .error import PatternError, PatternLockedError
 from .shapes import Shape
 from .label import Label
 from .subpattern import SubPattern
diff --git a/masque/error.py b/masque/error.py
index 8a67b6e..4a5c21a 100644
--- a/masque/error.py
+++ b/masque/error.py
@@ -7,3 +7,11 @@ class PatternError(Exception):
 
     def __str__(self):
         return repr(self.value)
+
+
+class PatternLockedError(PatternError):
+    """
+    Exception raised when trying to modify a locked pattern
+    """
+    def __init__(self):
+        PatternError.__init__(self, 'Tried to modify a locked Pattern, subpattern, or shape')
diff --git a/masque/file/gdsii.py b/masque/file/gdsii.py
index ad63711..f5ecc83 100644
--- a/masque/file/gdsii.py
+++ b/masque/file/gdsii.py
@@ -76,7 +76,7 @@ def write(patterns: Pattern or List[Pattern],
     :param library_name: Library name written into the GDSII file.
         Default 'masque-gdsii-write'.
     :param modify_originals: If True, the original pattern is modified as part of the writing
-        process. Otherwise, a copy is made.
+        process. Otherwise, a copy is made and deepunlock()-ed.
         Default False.
     :param disambiguate_func: Function which takes a list of patterns and alters them
         to make their names valid and unique. Default is `disambiguate_pattern_names`, which
@@ -90,7 +90,7 @@ def write(patterns: Pattern or List[Pattern],
         disambiguate_func = disambiguate_pattern_names
 
     if not modify_originals:
-        patterns = copy.deepcopy(patterns)
+        patterns = [p.deepcopy().deepunlock() for p in patterns]
 
     # Create library
     lib = gdsii.library.Library(version=600,
diff --git a/masque/label.py b/masque/label.py
index 3e2e8c7..d9fcd3e 100644
--- a/masque/label.py
+++ b/masque/label.py
@@ -3,7 +3,7 @@ import copy
 import numpy
 from numpy import pi
 
-from . import PatternError
+from .error import PatternError, PatternLockedError
 from .utils import is_scalar, vector2, rotation_matrix_2d
 
 
@@ -12,9 +12,9 @@ __author__ = 'Jan Petykiewicz'
 
 class Label:
     """
-    A circle, which has a position and radius.
+    A text annotation with a position and layer (but no size; it is not drawn)
     """
-    __slots__ = ('_offset', '_layer', '_string', 'identifier')
+    __slots__ = ('_offset', '_layer', '_string', 'identifier', 'locked')
     # [x_offset, y_offset]
     _offset: numpy.ndarray
 
@@ -27,6 +27,13 @@ class Label:
     # Arbitrary identifier tuple
     identifier: Tuple
 
+    locked: bool                # If True, any changes to the label will raise a PatternLockedError
+
+    def __setattr__(self, name, value):
+        if self.locked and name != 'locked':
+            raise PatternLockedError()
+        object.__setattr__(self, name, value)
+
     # ---- Properties
     # offset property
     @property
@@ -78,11 +85,20 @@ class Label:
     def __init__(self,
                  string: str,
                  offset: vector2=(0.0, 0.0),
-                 layer: int=0):
+                 layer: int=0,
+                 locked: bool = False):
+        self.unlock()
         self.identifier = ()
         self.string = string
         self.offset = numpy.array(offset, dtype=float)
         self.layer = layer
+        self.locked = locked
+
+    def __copy__(self) -> 'Label':
+        return Label(string=self.string,
+                     offset=self.offset.copy(),
+                     layer=self.layer,
+                     locked=self.locked)
 
     def  __deepcopy__(self, memo: Dict = None) -> 'Label':
         memo = {} if memo is None else memo
@@ -134,4 +150,20 @@ class Label:
         """
         return numpy.array([self.offset, self.offset])
 
+    def lock(self) -> 'Label':
+        """
+        Lock the Label
 
+        :return: self
+        """
+        object.__setattr__(self, 'locked', True)
+        return self
+
+    def unlock(self) -> 'Label':
+        """
+        Unlock the Label
+
+        :return: self
+        """
+        object.__setattr__(self, 'locked', False)
+        return self
diff --git a/masque/pattern.py b/masque/pattern.py
index 1de2f28..50d4e34 100644
--- a/masque/pattern.py
+++ b/masque/pattern.py
@@ -17,7 +17,7 @@ from .repetition import GridRepetition
 from .shapes import Shape, Polygon
 from .label import Label
 from .utils import rotation_matrix_2d, vector2, normalize_mirror
-from .error import PatternError
+from .error import PatternError, PatternLockedError
 
 __author__ = 'Jan Petykiewicz'
 
@@ -37,17 +37,19 @@ class Pattern:
             may reference the same Pattern object.
     :var name: An identifier for this object. Not necessarily unique.
     """
-    __slots__ = ('shapes', 'labels', 'subpatterns', 'name')
+    __slots__ = ('shapes', 'labels', 'subpatterns', 'name', 'locked')
     shapes: List[Shape]
     labels: List[Label]
     subpatterns: List[SubPattern or GridRepetition]
     name: str
+    locked: bool
 
     def __init__(self,
                  name: str = '',
                  shapes: List[Shape] = (),
                  labels: List[Label] = (),
                  subpatterns: List[SubPattern] = (),
+                 locked: bool = False,
                  ):
         """
         Basic init; arguments get assigned to member variables.
@@ -57,7 +59,9 @@ class Pattern:
         :param labels: Initial labels in the Pattern
         :param subpatterns: Initial subpatterns in the Pattern
         :param name: An identifier for the Pattern
+        :param locked: Whether to lock the pattern after construction
         """
+        self.unlock()
         if isinstance(shapes, list):
             self.shapes = shapes
         else:
@@ -74,14 +78,27 @@ class Pattern:
             self.subpatterns = list(subpatterns)
 
         self.name = name
+        self.locked = locked
+
+    def __setattr__(self, name, value):
+        if self.locked and name != 'locked':
+            raise PatternLockedError()
+        object.__setattr__(self, name, value)
+
+    def  __copy__(self, memo: Dict = None) -> 'Pattern':
+        return Pattern(name=self.name,
+                       shapes=copy.deepcopy(self.shapes),
+                       labels=copy.deepcopy(self.labels),
+                       subpatterns=[copy.copy(sp) for sp in self.subpatterns],
+                       locked=self.locked)
 
     def  __deepcopy__(self, memo: Dict = None) -> 'Pattern':
         memo = {} if memo is None else memo
-        new = copy.copy(self)
-        new.name = self.name
-        new.shapes = copy.deepcopy(self.shapes, memo)
-        new.labels = copy.deepcopy(self.labels, memo)
-        new.subpatterns = copy.deepcopy(self.subpatterns, memo)
+        new = Pattern(name=self.name,
+                shapes=copy.deepcopy(self.shapes, memo),
+                labels=copy.deepcopy(self.labels, memo),
+                subpatterns=copy.deepcopy(self.subpatterns, memo),
+                locked=self.locked)
         return new
 
     def append(self, other_pattern: 'Pattern') -> 'Pattern':
@@ -363,7 +380,7 @@ class Pattern:
         :return: A list of (Ni, 2) numpy.ndarrays specifying vertices of the polygons. Each ndarray
             is of the form [[x0, y0], [x1, y1],...].
         """
-        pat = copy.deepcopy(self).polygonize().flatten()
+        pat = self.deepcopy().deepunlock().polygonize().flatten()
         return [shape.vertices + shape.offset for shape in pat.shapes]
 
     def referenced_patterns_by_id(self) -> Dict[int, 'Pattern']:
@@ -564,11 +581,7 @@ class Pattern:
 
         :return: A copy of the current Pattern.
         """
-        cp = copy.copy(self)
-        cp.shapes = copy.deepcopy(cp.shapes)
-        cp.labels = copy.deepcopy(cp.labels)
-        cp.subpatterns = [copy.copy(subpat) for subpat in cp.subpatterns]
-        return cp
+        return copy.copy(self)
 
     def deepcopy(self) -> 'Pattern':
         """
@@ -588,6 +601,52 @@ class Pattern:
                 len(self.shapes) == 0 and
                 len(self.labels) == 0)
 
+    def lock(self) -> 'Pattern':
+        """
+        Lock the pattern
+
+        :return: self
+        """
+        object.__setattr__(self, 'locked', True)
+        return self
+
+    def unlock(self) -> 'Pattern':
+        """
+        Unlock the pattern
+
+        :return: self
+        """
+        object.__setattr__(self, 'locked', False)
+        return self
+
+    def deeplock(self) -> 'Pattern':
+        """
+        Recursively lock the pattern, all referenced shapes, subpatterns, and labels
+
+        :return: self
+        """
+        self.lock()
+        for ss in self.shapes + self.labels:
+            ss.lock()
+        for sp in self.subpatterns:
+            sp.deeplock()
+        return self
+
+    def deepunlock(self) -> 'Pattern':
+        """
+        Recursively unlock the pattern, all referenced shapes, subpatterns, and labels
+
+        This is dangerous unless you have just performed a deepcopy!
+
+        :return: self
+        """
+        self.unlock()
+        for ss in self.shapes + self.labels:
+            ss.unlock()
+        for sp in self.subpatterns:
+            sp.deepunlock()
+        return self
+
     @staticmethod
     def load(filename: str) -> 'Pattern':
         """
diff --git a/masque/repetition.py b/masque/repetition.py
index 2a9fa27..0c3234a 100644
--- a/masque/repetition.py
+++ b/masque/repetition.py
@@ -9,7 +9,7 @@ import copy
 import numpy
 from numpy import pi
 
-from .error import PatternError
+from .error import PatternError, PatternLockedError
 from .utils import is_scalar, rotation_matrix_2d, vector2
 
 
@@ -33,7 +33,8 @@ class GridRepetition:
                  '_b_vector',
                  '_a_count',
                  '_b_count',
-                 'identifier')
+                 'identifier',
+                 'locked')
 
     pattern: 'Pattern'
 
@@ -49,6 +50,7 @@ class GridRepetition:
     _b_count: int
 
     identifier: Tuple
+    locked: bool
 
     def __init__(self,
                  pattern: 'Pattern',
@@ -60,7 +62,8 @@ class GridRepetition:
                  rotation: float = 0.0,
                  mirrored: List[bool] = None,
                  dose: float = 1.0,
-                 scale: float = 1.0):
+                 scale: float = 1.0,
+                 locked: bool = False):
         """
         :param a_vector: First lattice vector, of the form [x, y].
             Specifies center-to-center spacing between adjacent elements.
@@ -70,6 +73,7 @@ class GridRepetition:
             Can be omitted when specifying a 1D array.
         :param b_count: Number of elements in the b_vector direction.
             Should be omitted if b_vector was omitted.
+        :param locked: Whether the subpattern is locked after initialization.
         :raises: InvalidDataError if b_* inputs conflict with each other
             or a_count < 1.
         """
@@ -85,6 +89,7 @@ class GridRepetition:
         if b_count < 1:
             raise InvalidDataError('Repetition has too-small b_count: '
                                    '{}'.format(b_count))
+        self.unlock()
         self.a_vector = a_vector
         self.b_vector = b_vector
         self.a_count = a_count
@@ -99,6 +104,12 @@ class GridRepetition:
         if mirrored is None:
             mirrored = [False, False]
         self.mirrored = mirrored
+        self.locked = locked
+
+    def __setattr__(self, name, value):
+        if self.locked and name != 'locked':
+            raise PatternLockedError()
+        object.__setattr__(self, name, value)
 
     def  __copy__(self) -> 'GridRepetition':
         new = GridRepetition(pattern=self.pattern,
@@ -110,7 +121,8 @@ class GridRepetition:
                              rotation=self.rotation,
                              dose=self.dose,
                              scale=self.scale,
-                             mirrored=self.mirrored.copy())
+                             mirrored=self.mirrored.copy(),
+                             locked=self.locked)
         return new
 
     def  __deepcopy__(self, memo: Dict = None) -> 'GridReptition':
@@ -126,6 +138,9 @@ class GridRepetition:
 
     @offset.setter
     def offset(self, val: vector2):
+        if self.locked:
+            raise PatternLockedError()
+
         if not isinstance(val, numpy.ndarray):
             val = numpy.array(val, dtype=float)
 
@@ -243,7 +258,7 @@ class GridRepetition:
         for a in range(self.a_count):
             for b in range(self.b_count):
                 offset = a * self.a_vector + b * self.b_vector
-                newPat = self.pattern.deepcopy()
+                newPat = self.pattern.deepcopy().deepunlock()
                 newPat.translate_elements(offset)
                 patterns.append(newPat)
 
@@ -343,3 +358,42 @@ class GridRepetition:
         """
         return copy.deepcopy(self)
 
+    def lock(self) -> 'GridRepetition':
+        """
+        Lock the GridRepetition
+
+        :return: self
+        """
+        object.__setattr__(self, 'locked', True)
+        return self
+
+    def unlock(self) -> 'GridRepetition':
+        """
+        Unlock the GridRepetition
+
+        :return: self
+        """
+        object.__setattr__(self, 'locked', False)
+        return self
+
+    def deeplock(self) -> 'GridRepetition':
+        """
+        Recursively lock the GridRepetition and its contained pattern
+
+        :return: self
+        """
+        self.lock()
+        self.pattern.deeplock()
+        return self
+
+    def deepunlock(self) -> 'GridRepetition':
+        """
+        Recursively unlock the GridRepetition and its contained pattern
+
+        This is dangerous unless you have just performed a deepcopy!
+
+        :return: self
+        """
+        self.unlock()
+        self.pattern.deepunlock()
+        return self
diff --git a/masque/shapes/arc.py b/masque/shapes/arc.py
index 92204a4..49c8fbe 100644
--- a/masque/shapes/arc.py
+++ b/masque/shapes/arc.py
@@ -147,7 +147,9 @@ class Arc(Shape):
                  rotation: float = 0,
                  mirrored: Tuple[bool] = (False, False),
                  layer: int = 0,
-                 dose: float = 1.0):
+                 dose: float = 1.0,
+                 locked: bool = False):
+        self.unlock()
         self.identifier = ()
         self.radii = radii
         self.angles = angles
@@ -159,6 +161,7 @@ class Arc(Shape):
         self.dose = dose
         self.poly_num_points = poly_num_points
         self.poly_max_arclen = poly_max_arclen
+        self.locked = locked
 
     def  __deepcopy__(self, memo: Dict = None) -> 'Arc':
         memo = {} if memo is None else memo
diff --git a/masque/shapes/circle.py b/masque/shapes/circle.py
index 5ee901f..f9b2192 100644
--- a/masque/shapes/circle.py
+++ b/masque/shapes/circle.py
@@ -44,7 +44,9 @@ class Circle(Shape):
                  poly_max_arclen: float = None,
                  offset: vector2 = (0.0, 0.0),
                  layer: int = 0,
-                 dose: float = 1.0):
+                 dose: float = 1.0,
+                 locked: bool = False):
+        self.unlock()
         self.identifier = ()
         self.offset = numpy.array(offset, dtype=float)
         self.layer = layer
@@ -52,6 +54,7 @@ class Circle(Shape):
         self.radius = radius
         self.poly_num_points = poly_num_points
         self.poly_max_arclen = poly_max_arclen
+        self.locked = locked
 
     def  __deepcopy__(self, memo: Dict = None) -> 'Circle':
         memo = {} if memo is None else memo
diff --git a/masque/shapes/ellipse.py b/masque/shapes/ellipse.py
index fba194a..7fe2c66 100644
--- a/masque/shapes/ellipse.py
+++ b/masque/shapes/ellipse.py
@@ -88,7 +88,9 @@ class Ellipse(Shape):
                  rotation: float = 0,
                  mirrored: Tuple[bool] = (False, False),
                  layer: int = 0,
-                 dose: float = 1.0):
+                 dose: float = 1.0,
+                 locked: bool = False):
+        self.unlock()
         self.identifier = ()
         self.radii = radii
         self.offset = offset
@@ -98,6 +100,7 @@ class Ellipse(Shape):
         self.dose = dose
         self.poly_num_points = poly_num_points
         self.poly_max_arclen = poly_max_arclen
+        self.locked = locked
 
     def  __deepcopy__(self, memo: Dict = None) -> 'Ellipse':
         memo = {} if memo is None else memo
diff --git a/masque/shapes/path.py b/masque/shapes/path.py
index d7ede07..7062fd5 100644
--- a/masque/shapes/path.py
+++ b/masque/shapes/path.py
@@ -151,7 +151,9 @@ class Path(Shape):
                  mirrored: Tuple[bool] = (False, False),
                  layer: int = 0,
                  dose: float = 1.0,
+                 locked: bool = False,
                  ) -> 'Path':
+        self.unlock()
         self._cap_extensions = None     # Since .cap setter might access it
 
         self.identifier = ()
@@ -165,6 +167,7 @@ class Path(Shape):
             self.cap_extensions = cap_extensions
         self.rotate(rotation)
         [self.mirror(a) for a, do in enumerate(mirrored) if do]
+        self.locked = locked
 
     def  __deepcopy__(self, memo: Dict = None) -> 'Path':
         memo = {} if memo is None else memo
diff --git a/masque/shapes/polygon.py b/masque/shapes/polygon.py
index a899229..02ac891 100644
--- a/masque/shapes/polygon.py
+++ b/masque/shapes/polygon.py
@@ -77,7 +77,9 @@ class Polygon(Shape):
                  mirrored: Tuple[bool] = (False, False),
                  layer: int = 0,
                  dose: float = 1.0,
+                 locked: bool = False,
                  ):
+        self.unlock()
         self.identifier = ()
         self.layer = layer
         self.dose = dose
@@ -85,6 +87,7 @@ class Polygon(Shape):
         self.offset = offset
         self.rotate(rotation)
         [self.mirror(a) for a, do in enumerate(mirrored) if do]
+        self.locked = locked
 
     def  __deepcopy__(self, memo: Dict = None) -> 'Polygon':
         memo = {} if memo is None else memo
diff --git a/masque/shapes/shape.py b/masque/shapes/shape.py
index 497e7e9..429e9dd 100644
--- a/masque/shapes/shape.py
+++ b/masque/shapes/shape.py
@@ -3,7 +3,7 @@ from abc import ABCMeta, abstractmethod
 import copy
 import numpy
 
-from .. import PatternError
+from ..error import PatternError, PatternLockedError
 from ..utils import is_scalar, rotation_matrix_2d, vector2
 
 
@@ -24,13 +24,26 @@ class Shape(metaclass=ABCMeta):
     """
     Abstract class specifying functions common to all shapes.
     """
-    __slots__ = ('_offset', '_layer', '_dose', 'identifier')
+    __slots__ = ('_offset', '_layer', '_dose', 'identifier', 'locked')
 
     _offset: numpy.ndarray      # [x_offset, y_offset]
     _layer: int or Tuple        # Layer (integer >= 0 or tuple)
     _dose: float                # Dose
     identifier: Tuple           # An arbitrary identifier for the shape,
                                 #  usually empty but used by Pattern.flatten()
+    locked: bool                # If True, any changes to the shape will raise a PatternLockedError
+
+    def __setattr__(self, name, value):
+        if self.locked and name != 'locked':
+            raise PatternLockedError()
+        object.__setattr__(self, name, value)
+
+    def __copy__(self) -> 'Shape':
+        cls = self.__class__
+        new = cls.__new__(cls)
+        for name in Shape.__slots__ + self.__slots__:
+            object.__setattr__(new, name, getattr(self, name))
+        return new
 
     # --- Abstract methods
     @abstractmethod
@@ -388,3 +401,20 @@ class Shape(metaclass=ABCMeta):
 
         return manhattan_polygons
 
+    def lock(self) -> 'Shape':
+        """
+        Lock the Shape
+
+        :return: self
+        """
+        object.__setattr__(self, 'locked', True)
+        return self
+
+    def unlock(self) -> 'Shape':
+        """
+        Unlock the Shape
+
+        :return: self
+        """
+        object.__setattr__(self, 'locked', False)
+        return self
diff --git a/masque/shapes/text.py b/masque/shapes/text.py
index f05e7bd..2d082d5 100644
--- a/masque/shapes/text.py
+++ b/masque/shapes/text.py
@@ -77,7 +77,10 @@ class Text(Shape):
                  rotation: float = 0.0,
                  mirrored: Tuple[bool] = (False, False),
                  layer: int = 0,
-                 dose: float = 1.0):
+                 dose: float = 1.0,
+                 locked: bool = False,
+                 ):
+        self.unlock()
         self.identifier = ()
         self.offset = offset
         self.layer = layer
@@ -87,6 +90,7 @@ class Text(Shape):
         self.rotation = rotation
         self.font_path = font_path
         self.mirrored = mirrored
+        self.locked = locked
 
     def  __deepcopy__(self, memo: Dict = None) -> 'Text':
         memo = {} if memo is None else memo
diff --git a/masque/subpattern.py b/masque/subpattern.py
index b8441d5..b2da81f 100644
--- a/masque/subpattern.py
+++ b/masque/subpattern.py
@@ -9,7 +9,7 @@ import copy
 import numpy
 from numpy import pi
 
-from .error import PatternError
+from .error import PatternError, PatternLockedError
 from .utils import is_scalar, rotation_matrix_2d, vector2
 
 
@@ -21,7 +21,8 @@ class SubPattern:
     SubPattern provides basic support for nesting Pattern objects within each other, by adding
      offset, rotation, scaling, and associated methods.
     """
-    __slots__ = ('pattern', '_offset', '_rotation', '_dose', '_scale', '_mirrored', 'identifier')
+    __slots__ = ('pattern', '_offset', '_rotation', '_dose', '_scale', '_mirrored',
+                 'identifier', 'locked')
     pattern: 'Pattern'
     _offset: numpy.ndarray
     _rotation: float
@@ -29,14 +30,18 @@ class SubPattern:
     _scale: float
     _mirrored: List[bool]
     identifier: Tuple
+    locked: bool
 
+    #TODO more documentation?
     def __init__(self,
                  pattern: 'Pattern',
                  offset: vector2 = (0.0, 0.0),
                  rotation: float = 0.0,
                  mirrored: List[bool] = None,
                  dose: float = 1.0,
-                 scale: float = 1.0):
+                 scale: float = 1.0,
+                 locked: bool = False):
+        self.unlock()
         self.identifier = ()
         self.pattern = pattern
         self.offset = offset
@@ -46,6 +51,12 @@ class SubPattern:
         if mirrored is None:
             mirrored = [False, False]
         self.mirrored = mirrored
+        self.locked = locked
+
+    def __setattr__(self, name, value):
+        if self.locked and name != 'locked':
+            raise PatternLockedError()
+        object.__setattr__(self, name, value)
 
     def  __copy__(self) -> 'SubPattern':
         new = SubPattern(pattern=self.pattern,
@@ -53,7 +64,8 @@ class SubPattern:
                          rotation=self.rotation,
                          dose=self.dose,
                          scale=self.scale,
-                         mirrored=self.mirrored.copy())
+                         mirrored=self.mirrored.copy(),
+                         locked=self.locked)
         return new
 
     def  __deepcopy__(self, memo: Dict = None) -> 'SubPattern':
@@ -130,7 +142,7 @@ class SubPattern:
          SubPattern's properties.
         :return: Copy of self.pattern that has been altered to reflect the SubPattern's properties.
         """
-        pattern = self.pattern.deepcopy()
+        pattern = self.pattern.deepcopy().deepunlock()
         pattern.scale_by(self.scale)
         [pattern.mirror(ax) for ax, do in enumerate(self.mirrored) if do]
         pattern.rotate_around((0.0, 0.0), self.rotation)
@@ -218,3 +230,43 @@ class SubPattern:
         :return: copy.copy(self)
         """
         return copy.deepcopy(self)
+
+    def lock(self) -> 'SubPattern':
+        """
+        Lock the SubPattern
+
+        :return: self
+        """
+        object.__setattr__(self, 'locked', True)
+        return self
+
+    def unlock(self) -> 'SubPattern':
+        """
+        Unlock the SubPattern
+
+        :return: self
+        """
+        object.__setattr__(self, 'locked', False)
+        return self
+
+    def deeplock(self) -> 'SubPattern':
+        """
+        Recursively lock the SubPattern and its contained pattern
+
+        :return: self
+        """
+        self.lock()
+        self.pattern.deeplock()
+        return self
+
+    def deepunlock(self) -> 'SubPattern':
+        """
+        Recursively unlock the SubPattern and its contained pattern
+
+        This is dangerous unless you have just performed a deepcopy!
+
+        :return: self
+        """
+        self.unlock()
+        self.pattern.deepunlock()
+        return self