After separating the electronic end nuclear coordinates through the Born-Oppenheimer approximation, one may attempt to solve the electronic Schrodinger equation by a hierarchy of wave function techniques. The lowest level in this hierarchy and the core method of the wave function quantum chemistry is the Hartree-Fock (HF) model, in which each electron moves in a mean field created by all other electrons. In order to get a chemical accuracy, one needs to correlate the motion of the electrons. This may be achieved by either the perturbation theory or by the configuration interaction procedure, employed on the top of the HF wave function. Basic ideas and approximations used in these wave function methods, as well as numerical approaches, challenges, and limitations will be discussed.