This book presents a detailed exposition of the formalism and application of k.p theory for both bulk and nanostructured semiconductors. For bulk crystals, this is the first time all the major techniques for deriving the most popular Hamiltonians have been provided in one place. For nanostructures, this is the first time the Burt-Foreman theory has been made accessible. Thus, the reader will gain a clear understanding of the k.p method, will have an explicit listing of the various Hamiltonians in a consistent notation for their use, and a set of representative results. In addition, the reader can derive an excellent understanding of the electronic structure of semiconductors.