This chapter deals with the various primary processes of island genesis (volcanic, tecto-orogenetic, sedimentary or coralline) before addressing secondary processes such as isostatic subsidence, emersion, marine ingression, erosion, horizontal and vertical drift as well as doming. In most cases islands are formed as a result of several processes, although this varies with island size: the smaller the island, the more likely it is that a single dominant process is responsible for its genesis. Examples are provided for each of the different island types.