diff --git a/esbo_etc/classes/__init__.py b/esbo_etc/classes/__init__.py
index 289e0c8..9cebda3 100644
--- a/esbo_etc/classes/__init__.py
+++ b/esbo_etc/classes/__init__.py
@@ -5,3 +5,4 @@ from .target import *
 from .optical_component import *
 from .RadiantFactory import *
 from .sensor import *
+from .psf import *
diff --git a/esbo_etc/classes/psf/IPSF.py b/esbo_etc/classes/psf/IPSF.py
new file mode 100644
index 0000000..dff152c
--- /dev/null
+++ b/esbo_etc/classes/psf/IPSF.py
@@ -0,0 +1,43 @@
+from abc import ABC, abstractmethod
+import astropy.units as u
+import numpy as np
+from typing import Union
+
+
+class IPSF(ABC):
+    """
+    Interface for modelling a PSF
+    """
+    @abstractmethod
+    def calcReducedObservationAngle(self, contained_energy: Union[str, int, float, u.Quantity]) -> u.Quantity:
+        """
+        Calculate the reduced observation angle in lambda / d_ap for the given contained energy.
+
+        Parameters
+        ----------
+        contained_energy : Union[str, int, float, u.Quantity]
+            The percentage of energy to be contained within a circle with the diameter reduced observation angle.
+
+        Returns
+        -------
+        reduced_observation_angle: Quantity
+            The reduced observation angle in lambda / d_ap
+        """
+        pass
+
+    @abstractmethod
+    def mapToGrid(self, grid: np.ndarray) -> np.ndarray:
+        """
+        Map the integrated PSF values to a sensor grid.
+
+        Parameters
+        ----------
+        grid : ndarray
+            The grid to map the values to. The values will only be mapped onto entries with the value 1.
+
+        Returns
+        -------
+        grid : ndarray
+            The grid with the mapped values.
+        """
+        pass