In this project report, we first present the application of the finite elements method to the numerical approximation of elliptic and parabolic PDEs over two-dimensional domains. We then consider the theory and numerical approximation of optimal control problems governed by elliptic and parabolic PDEs, implementing a steady and unsteady solver, using the Mlife library for Matlab. Finally, we apply the methods above to an inverse problem dealing with a problem of nuclear contamination.