From the mysterious depths of Lake Vostok, Antarctica, to tropical floodplain lakes, inland seas, hydro-reservoirs and the variety of waterbodies in our local environment, lakes encompass a huge diversity of shapes, sizes, depths, colours, and even salinities. Often very large and very deep, they sustain important and unique ecosystems which can be hotspots of biodiversity, and are used by humans as sources of drinking water and food, in particular, fish. What is theorigin of differences among lakes, and how does that affect the life within them? What are the seasons of a lake, and how do human actions alter lake ecosystems locally, and at a global scale? In this Very Short Introductions, Warwick Vincent outlines the essential features of lake environments and their biology, offering an up-to-date view of lake ecosystems. Vincent traces the origins of lake science (limnology) from the seminal work of Fran¿s Forel on Lake Geneva at the edge of the Swiss Alps, to modern approaches such a