The monograph is devoted to the theory of physical phenomena occurring in the planetary boundary layer of the atmosphere. In the first part of the book, the conclusion of equations describing the flow in the lower atmosphere is given. Semi-empirical hypotheses are discussed, on the basis of which a system of equations can be closed. The rest of the material is an application of the obtained equations to study the processes occurring in the boundary layer. Some applied problems are considered, the solution of which is significantly related to the specifics of the lower layers of the atmosphere.