This paper is a review of methods of generating molecular beams. Conventional effusion and gasdynamic sources are examined in detail and a comparative analysis is made of them. Methods of producing high-energy beams ( > 1 eV), an area of present intense development, are discussed at length. Particular attention is focused on fast molecular beams that contain atomic oxygen and are used for the study of physicochemical processes on solid surfaces (erosion, chemoluminescence).