This book presents the topological and analytical foundations of the theory of Maslov's canonical operator for finding asymptotic solutions of a wide class of pseudodifferential equations. The topology and geometry of Lagrangian manifolds are studied in detail and the connections between Fourier integral operators and canonical operators established. Applications are proposed for the asymptotic solutions to the Cauchy problem and for the asymptotics of the spectra of non-self-dual operators. The authors set out to make more accessible to a wider readership - of specialists in topology,...