This chapter presents the theoretical description and the principle of the operation of analysis and synthesis filter banks. This is essential material for understanding the modern design of transceivers that are based on discrete-time signal processing. The structure of a quadrature mirror filter bank is presented and the operation of the analysis and synthesis component filters is explained. The condition for a perfect reconstruction of a two-channel filter bank is derived. Based on a two-channel quadrature mirror filter bank, the procedure of making a multichannel quadrature mirror filter bank is presented. A brief description of multilevel filter banks with equal or unequal passband widths is given.