For a long time scientists, and in particular limnologists, have been interested in Lake Titicaca, a huge mass of tropical, though cold water, described as the largest navigable high-altitude lake in the world. This work assesses and summarizes the existing knowledge related to the main features of the lake: its geological origin, its slow evolution, the physical and chemical characteristics of its waters, its climate, hydrology, flora and fauna. And since it is difficult to dissociate this original biotope from the human component, which takes advantage of its resources, part of the book is dedicated to the socio-economic potential of Lake Titicaca and its littoral agriculture, as well as the human groups which in the past lived along the shoreline and on its islands. In spite of its extension and considerable water mass, Lake Titicaca constitutes a delicate ecosystem, less stable than it appears at first glance. The alteration of this aquatic environment by human actions is still low, with the exception of some shallow bays, poorly connected with the rest of the lake. Nevertheless, it is very important not to surpass the current state of pollution, and even to reduce it. It is also necessary to use carefully the natural biological and hydrological resources of this lake. The collection in this work of a large amount of limnological data should be usefull when planning further complementary studies on specific aspects which have not yet been sufficiently explored. It should also be useful for all organizations dealing with the gestion of the natural resources of the Bolivian-Peruvian Altiplano, providing them with the elements necessary for political decisions in that field.