The known classical results of the theory of convective flows are analyzed. Special attention is paid to thermodynamic and mechanical characteristics of media used in free convection experiments. Different types of heat sources and methods of stratification of the medium are considered. The results of experimental studies of Rayleigh-Benard and Benard-Marangoni convection are given. Alternative physical approaches to the description of convective phenomena and mathematical methods developed specifically for their solution are presented.