This lecture covers Post-Hartree Fock (HF) methods, such as Configuration Interaction (CI) and Møller Plesset Perturbation Theory (MPn), which are used to include electron correlation effects neglected by HF. The lecture explains how electron correlation impacts the accuracy of HF results, especially in weakly correlated systems. Exercises involve comparing HF, MPn, and CI in describing bond dissociation energies and assessing the influence of electron correlation on structural parameters.