Correlated Basis Functions theory is used to microscopically study the properties of strongly interacting nuclear systems. The first part of these lectures is devoted to the analysis of the inclusive responses of nuclear matter. In particular, the density response and the spin and electromagnetic (longitudinal and transverse) ones are studied in a non relativistic model which includes both central and tensor nucleon-nucleon correlations. The results are compared with the available data from medium and heavy nuclei. In the second part, the ground state (energy, density and momentum distribution) of doubly closed shell nuclei (with both N equal or different from Z) is investigated. The Fermi Hypernetted Chain equations are extended to these systems and their structure is examined in details. Results for semirealistic central potentials are given up to such heavy nuclei as Pb.