The present lecture notes cover a first course in th~ most common types of stratified flows encountered in Environ­ mental Hydraulics. Most of the flows are buoyancy flows, i.e. currents in which gravity acts on small density differences. Part I presents the basic concepts of stagnant, densit- stratified water, and of flowing non-miscible stratified fluids. The similarity to the (presumed) well-known open channel flow, subject to a reduced gravity, is illustrated. Part II treats the miscible density stratified flows. In outlining the governing equations, the strong coupling between the turbulence (the mixing) and the mean flow is emphasized. The presentation and discussions of the basic governing equa­ tions are followed by illustrative examples. Separate chapters are devoted to Dense Bottom Currents, Free Penetrative Convec­ tion, Wind-driven Stratified Flow, Horizontal Buoyancy Flow and Vertical jet/plumes. Part III presents some examples of practical problems solved on the basis of knowledge given in the present lecture notes. It is the author's experience that the topics treated in chapter 8 and in the subsequent chapters are especially well­ suited for self-tuition, followed by a study-circle. ACKNOWLEDGEMENT The author has benefited by the valuable help of his col­ legues at the Institute of Hydrodynamics and Hydraulic Engin­ eering, the Technical University of Denmark, especially our librarian Mrs. Kirsten Dj¢rup, our secretary Mrs. Marianne Lewis and our technical draftsman Mrs. Liselotte Norup.