This Perspective will look at the occurrence of polytypism in colloidal nanocrystals of metal chalcogenides. The low energy barrier between growth in wurtzite and zincblende crystal phases allows the occurrence of both in a single particle which has a dramatic influence on shape control. To date, various strategies have been employed to understand and control this phenomenon leading to a range of particle shapes across a wide range of semiconductor compositions from the archetypal cadmium selenide to the more recently studied compound copper chalcogenide nanocrystals such as dicopper zinc tin tetrasulfide and copper indium gallium selenide systems. The Perspective will also look at the control factors for polytypism in colloidal nanocrystals and the impact of polytypism on end-use applications.