diff --git a/aotools/functions/__init__.py b/aotools/functions/__init__.py
index c011ccb..eac9a66 100644
--- a/aotools/functions/__init__.py
+++ b/aotools/functions/__init__.py
@@ -2,3 +2,4 @@
 from .zernike import *
 from ._functions import *
 from .karhunenLoeve import *
+from .ell_zernike import *
diff --git a/aotools/functions/ell_zernike.py b/aotools/functions/ell_zernike.py
new file mode 100644
index 0000000..c92d138
--- /dev/null
+++ b/aotools/functions/ell_zernike.py
@@ -0,0 +1,133 @@
+#!/usr/bin/env python3
+
+import numpy as np
+from zernike import RZern
+import matplotlib.pyplot as plt
+from scipy.linalg import eig
+
+'''
+Normalised "Zernike" polynomials for the elliptical aperture.
+Based on Virendra N. Mahajan and Guang-ming Dai, "Orthonormal polynomials in wavefront analysis: analytical solution," J. Opt. Soc. Am. A 24, 2994-3016 (2007).
+'''
+
+class ZernikeEllipticalaperture:
+    def __init__(self, rmax, npix, a, b, l, ell_aperture=True, coeff=None):
+        self.rmax = rmax    #maximum radial order
+        self.npix = npix    #number of pixels for the map
+        self.a = a          #major semi-axis (normalised)
+        self.b = b          #minor semi-axis (normalised)
+        self.l = l          #number of elliptical modes (polynomials)
+        self.ell_aperture = ell_aperture  # Specify whether to use the elliptical aperture
+        self.coeff = coeff  # Coefficients for the Zernike modes (optional)
+        self.ell_aperture_mask = self.GenerateEllipticalAperture()
+        self.circular_zern = self.GetCircZernikeValue()
+        self.E = self.CalculateEllipticalZernike()
+
+    def GetCircZernikeValue(self):
+        '''
+        Get values of circular (standard) Zernike polynomials.
+
+        Return: zern_value
+        '''
+
+        zernike = RZern(self.rmax)
+        xx, yy = np.meshgrid(np.linspace(-1, 1, self.npix), np.linspace(-1, 1, self.npix))
+        rho = np.sqrt(xx**2 + yy**2)
+        theta = np.arctan2(yy, xx)
+        zernike.make_cart_grid(xx, yy)
+
+        zern_value = []
+        nterms = int((self.rmax + 1) * (self.rmax + 2) / 2)
+        for i in range(nterms):
+            zern_value.append(zernike.Zk(i, rho, theta))
+
+        zern_value = np.array(zern_value / np.linalg.norm(zern_value)).squeeze()
+        return zern_value
+
+    def CalculateEllipticalZernike(self):
+        '''
+        Calculate elliptical orthonormal polynomials as a product of the conversion matrix and circular zernike polynomials.
+
+        Return: E
+        '''
+        Z = self.GetCircZernikeValue()
+        M = self.M_matrix()
+        E = []  # Initialize a list to store E arrays for each l
+
+        for i in range(1, self.l + 1):
+            E_l = np.zeros(Z[0].shape)  # Initialize E with the same shape as Z[0]
+            for j in range(1, i + 1):
+                E_l += M[i - 1, j - 1] * Z[j - 1]
+            E.append(E_l)
+
+        E = np.array(E)
+        if self.ell_aperture:
+            E[:, np.logical_not(self.ell_aperture_mask)] = 0
+        return E
+
+    def M_matrix(self):
+        '''
+        Calculate the conversion matrix.
+
+        Return: M
+        '''
+        C = self.C_zern()
+        regularization = 1e-6  # Small positive constant to regularize
+        C += regularization * np.eye(C.shape[0])
+
+        Q = np.linalg.cholesky(C)
+        QT = np.transpose(Q)
+        M = np.linalg.inv(QT)
+        return M
+
+    def C_zern(self):
+        '''
+        Calculate C_zern matrix which is a symmetric matrix of inner products of Zernike polynomials
+        over the domain of a noncircular pupil (elliptical).
+
+        Return: C
+        '''
+        nterms = int((self.rmax + 1) * (self.rmax + 2) / 2)
+        # Initialize the C matrix
+        C = np.zeros((nterms, nterms))
+        # Calculate the area of each grid cell
+        dx = (2 * self.a) / 10000
+        dy = (2 * self.b) / 10000
+
+        for i in range(nterms):
+            for j in range(i, nterms):
+                product_Zern = np.dot(self.circular_zern[i], self.circular_zern[j]) * dx * dy
+                C[i, j] += np.sum(product_Zern)
+                if i != j:
+                    C[j, i] = C[i, j]
+
+        return C
+
+    def GenerateEllipticalAperture(self):
+
+        x, y = np.meshgrid(np.linspace(-1, 1, self.npix), np.linspace(-1, 1, self.npix))
+        normalized_distance = (x / self.a) ** 2 + (y / self.b) ** 2
+        aperture = (normalized_distance <= 1).astype(float)
+        return aperture
+
+    def EllZernikeMap(self, coeff=None):
+        '''
+        Generate a wavefront map on an elliptical pupil.
+        Parameters:
+        coeff (array): coefficients for the polynomial terms. Must be the same length as the number of elliptical modes.
+
+        Return: phi
+        '''
+        xx, yy = np.meshgrid(np.linspace(-1, 1, self.npix), np.linspace(-1, 1, self.npix))
+        E_ell = np.zeros((xx.size, self.l))
+
+        for k in range(self.l):
+            E_ell[:, k] = np.ravel(self.E[k])
+
+        if coeff is None:
+            coeff = np.random.random(self.l)
+
+        phi = np.dot(E_ell, coeff)
+        phi = phi.reshape(xx.shape)
+
+        return phi
diff --git a/test/test_ell_zernike.py b/test/test_ell_zernike.py
new file mode 100644
index 0000000..03472ed
--- /dev/null
+++ b/test/test_ell_zernike.py
@@ -0,0 +1,20 @@
+from aotools import functions
+import matplotlib.pyplot as plt
+
+if __name__ == '__main__':
+    a = 1
+    b = 0.8
+
+    rmax = 7
+    npix = 256
+    l = 35
+
+    ell_zern = functions.ZernikeEllipticalaperture(rmax, npix, a, b, l)
+
+    Ell = ell_zern.CalculateEllipticalZernike()
+    plt.imshow(Ell[2])
+    plt.show()
+
+    phi = ell_zern.EllZernikeMap()
+    plt.imshow(phi)
+    plt.show()