Agglomeration is a unit operation during which native particles are assembled to form bigger agglomerates, in which the original particle can still be distinguished. Agglomeration is considered to improve the functionality of food powders. Both physical and physicochemical phenomena must be considered when describing agglomeration. Food powders react when exposed to high temperatures and/or the addition of liquid, that is, their molecules can undergo irreversible physicochemical changes under these conditions. In this chapter, the agglomeration of food powders is described, from the generic concepts through to specifi citiesassociated with their physicochemical reactivity