This lecture covers the summary of lectures 1-2 in Solid State Physics II, focusing on topics such as Bloch theorem, Schrödinger equation in momentum space, Fermi surfaces of free electrons, tight-binding approximation, energy bands evolution, and experimental measurement of band structures using ARPES. The lecture also delves into the construction of Brillouin zones, band energy expressions, and the distinction between insulators and metals based on their band structures.