Many theories have been developed for predicting the vertical profiles of suspended sediment concentration in sediment-laden flows. An overview of various recent investigations is given herein. The generalization of the existing formulas and the interpretation of the typical sediment distributions are discussed in terms of continuum and kinetic concepts. The continuum assumption, which has been proved very successful for descriptions of liquid fluid motion, seems insufficient to describe motions of discrete solid particles in two-phase flows. Stochastic models can be used to approach the motion of the individual particles in the fluid, but are unsuitable for simulating interactions between solid particles. The analogy of kinetic theory in sediment-laden flows offers a promising alternative approach, and is expected for the applications in hyper-concentrated flow studies.