In this monograph, three-dimensional problems of acoustics and electrodynamics are investigated. Scalar problems of acoustic wave diffraction as well as vector problems of electromagnetic wave scattering are considered. The scatterers are finite systems of smooth screens, inhomogeneous solids, and partially shielded solids. Diffrac-tion problems (in differential and integral formulation) are investigated using pseudodifferential calculus and integral equations method. Monograph can be used by scientific researchers, postgrad-uate and graduate students who investigate boundary value problems, integral equations, and problems of diffraction of acoustic or elec-tromagnetic waves.