This book discusses selected theoretical topics of coastal hydrodynamics, including basic principles and applications in coastal oceanography and coastal engineering. It is not intended as a handbook; the emphasis is placed on presentation of a number of basic problems, rather than giving detailed instructions for their application. The bulk of the material deals with surface waves. In the author's opinion there is still a strong need for a book on wave phenomena in the coastal waters, as general textbooks on sea surface dynamics focus most of their attention on the deep ocean. This book intends to fill this need by concentrating on the phenomena typical of the coastal zone. Based on lectures given at the Institute of Hydroengineering, Polish Academy of Sciences in Gdansk, the approach throughout is a combination of the theoretical and observational. A basic knowledge of ordinary and partial differential equations, as well as the statistical and spectral analysis of time series, is assumed. The reader should also be familiar with fundamental hydrodynamic concepts. The book comprises nine chapters. Governing equations and conservation laws are treated in Chapter 1, using the variational principles. The theory of regular surface waves is covered in Chapters 2 to 4. The nonlinear effect of wave train modulation and their breaking of beaches is examined in Chapter 5. Chapters 6 and 7 focus on the statistical and spectral treatment of waves induced by wind. Current generation and circulation pattern are the subject of Chapter 8, while sea level variations are examined in Chapter 9. References for further reading are given at the end of each chapter.