This chapter describes the mechanisms by which tides may be deformed or distorted or rectified (all terms referring to the same phenomenon) when they enter semienclosed basins. The chapter first presents qualitative and quantitative arguments for the presence of distortions and the generation of high-frequency harmonics, that is, of periodicities in the tide that are shorter than the fundamental (semidiurnal and diurnal) tidal periods. The chapter continues by exploring the possibilities of the generation of high-frequency harmonics in what are referred to as shallow-water tides. These shallow-water tides can be overtides or compound tides, depending on what harmonics generate them. The chapter goes further with an explanation of the physical meaning of processes causing distortions. It concludes by providing a pair of examples of overtides and compound tides.