This book contributes to a better understanding of limnology, a discipline of ecology that studies continental aquatic ecosystems (stagnant and running waters). Intended for graduate students in environmental sciences (aquatic ecology in particular), it is structured in 3 essential parts: presentation of biological diversity, and the threats that impact on aquatic biodiversity; lentic environments (lakes, ponds, pools); and lotic environments (rivers, streams). This book provides the basic notions needed to teach limnology, as well as a useful reference for users of aquatic ecosystems.