Bloch's Theorem is a fundamental principle in solid-state physics that describes the behavior of electrons in a periodic potential, such as that found in crystals. It states that the wave functions of electrons can be expressed as a product of a plane wave and a function that has the same periodicity as the crystal lattice. This means that the electron states are organized into bands, which are crucial for understanding electrical conductivity and other properties of materials. The theorem is named after the physicist Felix Bloch, who formulated it in 1928. It provides a framework for analyzing the electronic structure of solids, allowing scientists to predict how materials will behave under various conditions. By applying Bloch's Theorem, researchers can better understand phenomena like semiconductors, superconductors, and the overall behavior of electrons in different materials.