Recent experimental studies of kinetic processes in dense gases and in plasma have stimulated the development of the theory of nonideal gases or plasmas. By now, a kinetic theory has been developed for nonideal monatomic gases of medium density, as well as a kinetic theory of weakly nonideal fully ionized plasma. The present review is devoted to a systematic exposition of these questions. The kinetic theory of nonideal gases of low density is constructed on the basis of a generalized Boltzmann kinetic equation (in the pair-collision approximation) and the Cho-Uhlenbeck kinetic equation (in the triple-collision approximation). The kinetic equations for denser gases have an essentially different structure than the ordinary kinetic equations. This is caused by the impossibility of using the ordinary scheme, owing to the divergences of the collision integrals in the higher approximations in the density. The article presents a kinetic theory of a weakly nonideal plasma. Particular attention is paid to the possibility of constructing classical and quantum kinetic equations without assuming the particle interaction to be small at short distances, since the particle interaction at short distances plays an essential role in a nonideal plasma. A. prominent place is occupied in the review by an exposition of the kinetic theory of fluctuations in nonideal gases and plasma. Certain problems in the kinetic theory of nonideal systems are considered.