This chapter begins with a general introduction to the Lagrangian methods, which provide a quantitative description of both track and speed of water current flow. These methods are employed to obtain an overall picture of oceanic currents and gyres over large as well as restricted areas. This discussion is followed by a description of various kinds of freely drifting surface drogues used for such measurements. These include drifter-following radar transponders, drifter-borne Doppler transponders, radio buoys tracked by polar-orbiting satellites, GPS-tracked drifters, and telephonically tracked drifters. This chapter winds up with a brief analysis of the limitations of surface drifters. Lists of references and bibliography are also provided for the benefit of the readers.