The textbook corresponds to the program of courses "Functional Analysis," "Theory of Operators," "Analysis III," which are taught at universities and pedagogical universities. The book contains the main set-theoretic concepts, presents the general theory of metric, topological, linear topological and normalized spaces, the general theory of measure, measurable functions and the Lebesgue integral. The theory of operators in Hilbert space, the spectral theory of self-adjoint operators, the application of the methods of the theory of analytic functions in the spectral theory of non-self-adjoint operators, the theory of Fourier transform and generalized functions are considered in detail.