We study linear problems of mathematical physics in which the adiabatic approximation is used in the wide sense. Using the idea that all these problems can be treated as problems with operator-valued symbol, we propose a general regular scheme of adiabatic approximation based on operator methods. This scheme is a generalization of the Born-Oppenheimer and Maslov methods, the Peierls substitution, etc. The approach proposed in this paper allows one to obtain "effective" reduced equations for a wide class of states inside terms (i.e., inside modes, subregions of dimensional quantization, etc.) with the possible degeneration taken into account. Next, applying the asymptotic methods in particular, the semiclassical approximation method, to the reduced equation, one can classify the states corresponding to a distinguished term (effective Hamiltonian). We show that the adiabatic effective Hamiltonian and the semiclassical Hamiltonian can be different, which results in the appearance of "nonstandard characteristics" while one passes to classical mechanics. This approach is used to construct solutions of several problems in wave and quantum mechanics, in particular, problems in molecular physics, solid-state physics, nanophysics, hydrodynamics.