PrefaceThe geometric study of flows on manifolds has a long history in mathematics, even though it was not considered as a special field until it appeared in the works of Poincar4, Lyapunov, and Bendixon. After that, the subject developed rapidly, and, at the present time, it is the focus of extensive research.It is impossible to touch upon all sides of the geometric theory of flows in one article. The purpose of this review is to present some aspects of the geometric theory of flows on 2-manifolds (of course, within the frame of our knowledge). Our main interest is the topological structure and the topological equivalence of surface flows, asymptotic properties of semitrajectories and the closing lemma, etc. (see the contents).However, our article was not written for specialists only; we have also attempted to provide an introduction to the subject.We would like to thank the many mathematicians who took part in valuable discussions of problems of the theory of dynamical systems, and especially D. Anosov, I. Bronshtein, V. Grines, G. Levitt, M. Malkin, Shigenory Matsumoto, I. Nikolaev, and A. Zorlch.