Many attempts have been made to explain the diversity of coastal environments using genetic or descriptive criteria, or a mixture of the two. This chapter explores the importance of variations in geological structure, sea level history and biogeography in providing contexts within which both contemporary ecological and geomorphological processes act and future environmental changes will be placed. Tectonics and sea level history provide the contexts for the operation of contemporary processes. Tides are a vital component of coastal dynamics, producing important currents and sediment movements, as well as influencing the zonation of coastal organisms, landforms and weathering processes. Tidal range is an important control on coastal ecology and geomorphology, determining the width of coast subjected to alternate wetting and drying and the impact of waves. Waves and tides provide the major controls on most coastal processes, other forms of water are important in coastal ecology and geomorphology.