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 For many food powders, the presence of moisture can change and compromise product performance as well as mixing and handling behavior. Food powders such as sugar, salt, whey, flour, starch and gravy mixes can all change due to uptake of moisture from a free-flowing powder to a caked, lumpy solid mass that does not flow at all. An overview of researches on the effect of moisture/water activity on powder flow behavior on selected food powders and comparative results on the changes in powder flow properties of these food powders using three types of powder flowability testers will be presented. The process of identifying critical moisture/Aw levels for different types of food powders when drastic changes in powder flow occur will also be discussed. Powder flowability is affected by a number of intrinsic and extrinsic factors such as physical attributes of the powder (moisture content/Aw, particle size, shape, hygroscopicity, cohesion, particle interaction, etc.), and environmental conditions (humidity, temperature). This presentation hopes to clarify how moisture sorption or moisture uptake influences flow behavior and the impact of these changes in powder properties on processes such as mixing, filling, compression, powder application (e.g. adhesion) and other processes.