Knowledge of turbulent mixing by plumes and jets, such as those encountered in smokestack emissions, volcanic eruptions, and sewage discharges, is important for controlling environmental impact and for assessing risk. Lee (civil engineering, U. of Hong Kong) and Chu (civil engineering and applied mechanics, McGill U., Canada) develop a Lagrangian approach to model turbulent jets and plumes, beginning with simple problems, and advancing toward the practical case of a turbulent buoyant jet in a density-stratified cross flow. The text will be of use to engineers and students studying hydraulics and environmental fluid mechanics.