In this paper, the literature on studying axisymmetric and nonaxisymmetric vibration of complete spherical shells, with and without imperfections, are thoroughly reviewed.Without considering the high order shear modes, there are two branches of vibration modes in spherical shells i.e.membrane modes (upper branch) and composite modes (lower branch).The membrane modes are purely extensional (membrane), whereas the composite modes are combined bending-extensional.The values of natural frequencies can be calculated analytically using the bending theory and the mode shapes can be expressed in Legendre Polynomials.