The late Professor G. N. Watson wrote his monumental treatise on the theory of Bessel functions with two objects in view. The first was the development of applications of the fundamental processes of the theory of complex variables; and the second was the compilation of a collection of results of value to mathematicians and physicists, who encounter Bessel functions in the course of their researches. The completeness of his theoretical account, combined with the wide scope of the practical examples and the extensive numerical tables, have resulted in a book which is indispensable to pure and applied mathematicians, as well as to physicists.