diff --git a/gprMax/user_objects/rotatable.py b/gprMax/user_objects/rotatable.py
new file mode 100644
index 00000000..d29f689e
--- /dev/null
+++ b/gprMax/user_objects/rotatable.py
@@ -0,0 +1,43 @@
+from abc import ABC, abstractmethod
+from typing import Optional, Tuple
+
+
+class Rotatable(ABC):
+    """Stores parameters and defines an interface for rotatable objects.
+
+    Attributes:
+        axis (str): Defines the axis about which to perform the
+            rotation. Must have value "x", "y", or "z". Default x.
+        angle (int): Specifies the angle of rotation (degrees).
+            Default 0.
+        origin (tuple | None): Optional point about which to perform the
+            rotation (x, y, z). Default None.
+        do_rotate (bool): True if the object should be rotated. False
+            otherwise. Default False.
+    """
+
+    def __init__(self):
+        self.axis = "x"
+        self.angle = 0
+        self.origin = None
+        self.do_rotate = False
+
+    def rotate(self, axis: str, angle: int, origin: Optional[Tuple[float, float, float]] = None):
+        """Sets parameters for rotation.
+
+        Args:
+            axis: Defines the axis about which to perform the rotation.
+                Must have value "x", "y", or "z".
+            angle: Specifies the angle of rotation (degrees).
+            origin: Optional point about which to perform the rotation
+                (x, y, z). Default None.
+        """
+        self.axis = axis
+        self.angle = angle
+        self.origin = origin
+        self.do_rotate = True
+
+    @abstractmethod
+    def _do_rotate(self):
+        """Performs the rotation."""
+        pass
diff --git a/gprMax/user_objects/user_objects.py b/gprMax/user_objects/user_objects.py
new file mode 100644
index 00000000..7bddeb02
--- /dev/null
+++ b/gprMax/user_objects/user_objects.py
@@ -0,0 +1,127 @@
+from abc import ABC, abstractmethod
+from typing import List, Union
+
+from gprMax import config
+from gprMax.grid.fdtd_grid import FDTDGrid
+from gprMax.grid.mpi_grid import MPIGrid
+from gprMax.model import Model
+from gprMax.subgrids.grid import SubGridBaseGrid
+from gprMax.user_inputs import MainGridUserInput, SubgridUserInput
+
+
+class UserObject(ABC):
+    """User defined object.
+
+    Attributes:
+        order (int): Specifies the order user objects should be
+            constructed in.
+        hash (str): gprMax hash command used to create the user object
+            in an input file.
+        kwargs (dict): Keyword arguments used to construct the user
+            object.
+        autotranslate (bool): TODO
+        is_single_use (bool): True if the object can only appear once in a
+            given model. False otherwise. Default True.
+        is_geometry_object (bool): True if the object adds geometry to the
+            model. False otherwise. Default False.
+    """
+
+    @property
+    @abstractmethod
+    def order(self) -> int:
+        pass
+
+    @property
+    @abstractmethod
+    def hash(self) -> str:
+        pass
+
+    @property
+    def is_single_use(self) -> bool:
+        return True
+
+    @property
+    def is_geometry_object(self) -> bool:
+        return False
+
+    def __init__(self, **kwargs) -> None:
+        self.kwargs = kwargs
+        self.autotranslate = True
+
+    def __str__(self) -> str:
+        """Readable user object as per hash commands."""
+        args: List[str] = []
+        for value in self.kwargs.values():
+            if isinstance(value, (tuple, list)):
+                for element in value:
+                    args.append(str(element))
+            else:
+                args.append(str(value))
+
+        return f"{self.hash}: {' '.join(args)}"
+
+    def _params_str(self) -> str:
+        """Readable string of parameters given to object."""
+        return f"{self.hash}: {str(self.kwargs)}"
+
+    def _create_uip(self, grid: FDTDGrid) -> Union[SubgridUserInput, MainGridUserInput]:
+        """Returns a point checker class based on the grid supplied.
+
+        Args:
+            grid: Grid to get a UserInput object for.
+
+        Returns:
+            uip: UserInput object for the grid provided.
+        """
+
+        # If autotranslate is set as True globally, local object
+        # configuration trumps. I.e. User can turn off autotranslate for
+        # specific objects.
+        if (
+            isinstance(grid, SubGridBaseGrid)
+            and config.sim_config.args.autotranslate
+            and self.autotranslate
+        ):
+            return SubgridUserInput(grid)
+        else:
+            return MainGridUserInput(grid)
+
+
+class MultiUserObject(UserObject):
+    """User defined object that can occur multiple times."""
+
+    @property
+    def is_single_use(self) -> bool:
+        return False
+
+
+class ModelUserObject(UserObject):
+    """User defined object to add to the model."""
+
+    @abstractmethod
+    def build(self, model: Model):
+        pass
+
+
+class GridUserObject(MultiUserObject):
+    """User defined object to add to a grid."""
+
+    @abstractmethod
+    def build(self, grid: FDTDGrid):
+        pass
+
+
+class OutputUserObject(MultiUserObject):
+    """User defined object that controls the output of data."""
+
+    @abstractmethod
+    def build(self, model: Model, grid: FDTDGrid):
+        pass
+
+
+class GeometryUserObject(GridUserObject):
+    """User defined object that adds geometry to a grid."""
+
+    @property
+    def is_geometry_object(self) -> bool:
+        return True