Because of a turbulent and complex recent geological history, New Zealand has an impressively diverse and dynamic landscape, and a correspondingly wide array of lake types, within a small land area (Irwin 1975a; Soons & Selby 1982;). The development of such an active geological environment in New Zealand has been governed largely by its location athwart the Australian and Pacific plate boundary, and its maritime mid-latitude position has made it particularly sensitive to the climatic fluctations and associated glaciations and sea level changes of the Quaternary Period (Suggate et al. 1978). At present, the rates of uplift and erosion of mountainous areas are among the fastest in the world. Earthquakes are common, and volcanism has characterised much of the North Island during the Quaternary with numerous volcanoes active in the last few thousand years. Large, explosive caldera volcanoes in central North Island have erupted repeatedly over the last million years, producing voluminous amounts of lava and widespread pyroclastic deposits. The landforms, soils and lakes are thus typically youthful, almost all being younger than two million years; indeed, much of the landscape is of late Pleistocene and Holocene age, and is still actively developing (Pillans et al. 1982). Our purpose in this chapter is to outline the relationship between these often violent and spectacular geological processes which have led to the formation and development of the various lake types in New Zealand. Against this background we describe the classification and distribution of the main lake types, their ages and mechanisms of formation. We also comment on lake sedimentation patterns, palaeolimnological studies, and on features of lake bathymetry and morphology.