Abstract 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, employed to obtain an overall picture of oceanic subsurface currents and gyres over large areas. This is followed by a description of different kinds of freely drifting subsurface floats used for such measurements. These consist of surface-trackable subsurface drifters, satellite-recovered pop-up drifters, Swallow floats tracked by ship-borne hydrophones, subsurface floats transmitting to moored acoustic receivers, subsurface floats listening to moored acoustic sources, horizontally displaced and vertically cycling subsurface float (ALACE), and drifting profiling floats (ARGO floats) that allow estimation of geostrophic currents at various depths from repeat profiles of water temperature, salinity, and depth data (density data). A brief account of profiling observations from polar regions is also provided.