Many of the large lakes of the world have been exposed to the introduction of exotic species. We have reviewed here the introduction of aquatic species in 18 large lakes on five continents (Laurentian Great Lakes, African Great Lakes, several Canadian lakes, Lake Titicaca, Lake Baikal, Lake Ladoga, Gatun Lake, and Lake Biwa). We found that human activities, social preferences, and policy decisions are often associated with the spread of species in these large lakes. However, the spread and resulting ecological effects of introduced species varied among the case studies reviewed (ranging from the failure of brown trout introduction in Lake Titicaca to successful introduction of Nile Perch in Lake Victoria). Those species that did establish successful populations often had major impacts upon the ecosystems of these lakes via a variety of processes, including predation, disturbance, habitat modification and competition. Although introduction of predators often negatively impacted native species (e.g. Nile perch in Lake Victoria, peacock bass in Lake Gatun), species introduced to lower trophic levels (e.g. sardine in Lakes Kariba and Kivu, rainbow smelt in Canadian Lakes) affected fisheries and altered food web structure as well. Exotic species in large lakes of the world were not limited to fish species: plants (e.g. in Lakes Baikal and Biwa), invertebrates (e.g. in Lake Ladoga), and parasites and pathogens (e.g. in Lake Titicaca) have been introduced, but it was often difficult to discern the food web and ecosystem effects of these organisms. Exotic species also impacted socio-economic systems, having both positive (e.g. Lakes Victoria, Titicaca, Kivu, and Kariba, and the Laurentian Great Lakes) and negative (e.g. Lakes Victoria and Titicaca, and the Laurentian Great Lakes) repercussions for humans who depended upon these lakes for food and income. Unfortunately, our understanding of the impacts and extent of introductions on large lake ecosystems often remains speculative at best. The introduction and spread of exotic species will continue to threaten large lakes of the world into the twenty-first century. Exotic species introductions are a global problem that deserves global attention and understanding.