Modern Problems in Condensed Matter Sciences, Volume 22.1: Spin Waves and Magnetic Excitations, Part I focuses on the principles, methodologies, approaches, and reactions involved in spin waves and magnetic excitations, including, Brillouin-Mandelstam light scattering, optical magnetic excitations, and magnetic dielectrics. The selection first elaborates on spin waves in magnetic dielectrics current status of the theory and light scattering from spin waves. Discussions focus on magneto-optic effects and the mechanism of light scattering in magnets, Brillouin-Mandelstam light scattering, Raman scattering, Collinear Heisenberg ferromagnet, low-temperature phase transitions, and low-dimensional systems. The text then ponders on optical magnetic excitations, spin waves above the threshold of parametric excitations, and theory of spin excitations in rare earth systems. Topics include Hamiltonian for rare earth systems, parametric instability of spin waves in magnetic dielectrics, nonstationary processes in parametric excitation of spin waves, radiative decay of magnetic excitons, and mechanism of the generation of magnetic excitations by light. The book tackles 4f moments and their interaction with conduction electrons and neutron scattering studies of magnetic excitations in itinerant magnets, including magnetic excitations at finite and low temperatures, paramagnetic scattering, coupling to conduction electrons, and virtual magnetic excitations. The selection is highly recommended for researchers wanting to study spin waves and magnetic excitations.