Limnology is one of the oldest disciplines and its subject is fresh waters. Here, information were given about development of limnology in the world and in Turkey and its current importance. Particularly, increasing importance of this discipline in the world and in Turkey was emphasized due to effects of global climate change on fresh waters. Subjects, limnologists have to primarily study in Turkey, were mentioned. Furthermore, subjects of "30th World Limnology Congress", which was organized in Canada, in 2007, were summarized.