The subject of boundary layers, a key topic of fluid mechanics, has featured for many years in university courses in aeronautical, mechanical and civil engineering. Drag and loading predictions for example and the consequent scope for drag reduction have important implications for aeronautical design and fuel reduction. However, there are surprisingly few text books devoted to boundary layers and little available to students on the important recent developments which have occurred as a result of the use of increasingly poweful computers. This new book will provide a succinct introduction to the subject, covering the fundamental physical ideas of laminar and turbulent boundary layers, assuming no prior knowledge of the subject. The main focus will be on two-dimensional flow, compressible as well as incompressible, but there will be some discussion of the special features of boundary layers in three dimensions.