The 10 largest lakes in the world hold 60 percent of our planet’s surface fresh water. People are drawn to their shores for ready access to clean water, abundant fish, inexpensive transportation, and an appealing lifestyle. Many of the world’s great lakes share a common threat of dropping lake level: in January 2013, Lake Michigan was at its lowest stand in recorded history, while the levels of many of the East African Rift Valley lakes will soon be threatened by expanding irrigation in their catchments. At the same time, the North American and African Great Lakes are experiencing contrasting changes in biodiversity, which is increasing in the Laurentian Great Lakes due to invasive species and decreasing in the African Rift lakes due to over fishing and habitat degradation. In this session we explore the evolution of some great lakes ecosystems on different time scales, beginning with the latest results from the Lake Malawi (East Africa) Drilling Project, a remarkable history of cichlid fish evolution in the African tropics, and the dramatic shift in ecosystem structure of Lake Michigan and the other Laurentian Great Lakes that resulted from the introduction of exotic species. Our means of detecting ecosystem change in the world’s great lakes continue to improve, and some of the new approaches will be described. The session will include a discussion among the speakers and audience regarding implications for future management of these invaluable aquatic resources.