Abstract The electronic structure of the strongly correlated system La 2CuO 4 is calculated, using a realistic tight-binding model for the electronic states in the Copper Oxide planes. The model includes the Oxygen p (x) and p (y) orbitals and the Copper 3 d (x 2−y 2)orbitals. The hybridization between the Copper d (x 2−y 2)and the Oxygen p (x) and p (y) orbitals is considered, as well as the direct overlap between the p orbitals of neighboring Oxygen ions. The Coulomb interaction between the electrons in the d shell of the Copper ions is treated by introducing slave bosons, thereby restricting the allowed Cu ionic configurations in the system to be Cu + +and Cu +. The system may exhibit a phase characterized by the participation of the d electrons in coherent itinerant states. However, there also exists the possibility of another phase characterized by the localization of the d electrons. This second phase occurs when the bare charge transfer energy is sufficiently large. Thus, for the stochiometric system there are two possible zero temperature states; a metallic state and a charge transfer insulator state. The p-p hopping matrix element is large and it is found that its sign, relative to the other hopping matrix elements, has a significant effect on the position of the phase boundary. Inferring values tight-binding integrals from band structure calculations, one concludes that the paramagnetic phase of La 2CuO 4 should be metallic. The electronic structure and Fermi-surface are calculated for this phase. The presence of long ranged anti-ferromagnetic order is expected to open up a Slater gap at the Fermi-energy, yielding the experimentally observed low temperature insulating phase.