This chapter develops the foundation for describing charged quasiparticles—electrons and holes—in semiconductors. The band structure E(k), introduced in Chap. 2 , is used to qualitatively establish the occupancy of electronic states in equilibrium and to understand band-to-band excitation in direct and indirect bandgap semiconductors. The emerging picture of excited states naturally leads to the concept of the hole, a positively charged quasiparticle introduced to represent the collective behavior of the valence band electrons. The clarification of the energy scales for electrons and holes is followed by an overview of basic concepts of electrostatics. The chapter ends with an introduction to excitons, i.e., electrically neutral quasiparticles in semiconductors.