Turbulence, the most important factor in the suspension of sediment, is defined and examined in this contribution to the proposed Report on Sedimentation Engineering. The diffusion mechanism is examined. The differential equation for the suspension of sediment is derived, as well as the classical equations for the distribution of suspended sediment in a turbulent flow. The agreement between the suspended load distribution equation and measurement of suspended load and the effect of suspended sediment on flow characteristics is examined. Several modifications of the classical theory of suspensions are presented and discussed briefly.