Viscosity is an important physical property of protein dispersions, which is defined as the internal resistance to flow. This is a crucial property of protein dispersions as it influences the overall acceptability and mouthfeel of the finished product. The understanding of viscosity helps in the appropriate selection of pumps and other process equipment. In addition, it is also critical to understand how various process parameters affect the flow behavior of protein dispersions. The viscosity of plant protein dispersions is influenced by pH, protein concentration, temperature, ionic strength and thermal history, etc. This chapter discusses the measurement of viscosity as a function of shear. Pea protein and soy protein isolates were used as examples of plant proteins, and a detailed analysis of viscosity and flow behavior is elaborated in this chapter.