Basics concepts of the tides are discussed: the tidal movement of sea level, tidal currents, the tide as a wave phenomenon. A qualitative explanation of tidal generation is given. The connection between tidal dissipation and changes in the length of day and lunar recession is explained. An example of a tide-gauge record serves to illustrate the main semidiurnal signal, the spring-neap cycle, and the diurnal inequality. The chapter is concluded with a discussion on the scope of the book and an overview of the contents of the chapters, followed by a further reading section.