In this book, we give a detailed construction of the crossed product of a C -algebra by a locally compact group. In Chapter 1, we review some preliminary results on locally compact groups and C -algebras. In Chapter 2, Haar measures on locally compact groups are studied and a brief harmonic analysis is discussed. In Chapter 3, we study vector-valued integration on groups and prove a version of the Fubini theorem for vector- valued integrals. In Chapter 4, transformation groups are considered, and C -dynamical systems and their covariant representations are investigated. Finally, we explore in Chapter 5 the construction of crossed products of C -algebras and provide some examples of crossed products. Some representations associated with crossed products are also briefly discussed