Francis D. Murnaghan, a distinguished contributor in the sphere of applied mathematics, created this comprehensive introduction to the theory of group representations. Murnaghan's first-rate account of the field pioneered and developed chiefly by Frobenius, Weyl, and Schur devotes particular attention to the groups--mainly the symmetric group and the rotation group--of fundamental significance for quantum mechanics (especially nuclear physics). Because groups of matrices are the usual group representations, this work is also a valuable contribution to the literature on matrices. The author places particular emphasis on such topics as the theory of group integration, the theory of two-valued or spin representations, the representations of the symmetric group and the analysis of their direct products, the crystallographic groups, and the Lorentz group and the concept of semivectors. Other sections cover groups and matrices, reducibility, group characters, the alternating group, linear groups, and the orthogonal group. This authoritative exposition is of specific interest to teachers and graduate-level students of applied mathematics, physics, and higher algebra.