This introductory chapter explores links between Lake Tanganyika, East Africa, and the wider Indian Ocean World in history and historiography. It does so firstly by stressing the peculiarities of Lake Tanganyika’s shape and environment in the East African context. It then draws on a wider historiography of lakes and oceans in world history, and it argues that doing so necessitates taking on perspectives from the wider Indian Ocean World. But, far from being a place where patterns from the wider Indian Ocean World replicated themselves, Lake Tanganyika was a ‘frontier’ where phenomena traditionally associated with the macro-region (including e.g. Islam, boating technologies, and fashions) were negotiated and reimagined in particularly robust ways. This applies especially to the period c.1830–90, during which coastal and Great Lakes populations encountered each other in significant numbers for the first time, caused by the expansion of the global ivory trade.