Phagocytosis is an essential component of the innate immune response. Invading microorganisms are engulfed by neutrophils and macrophages, and subsequently killed by a complex series of reactions that require fusion of the phagocytic vacuole with multiple endomembrane organelles. This vacuolar remodeling process, known as phagosomal maturation, is often the target of intracellular parasites that evade killing by the host immune system. This unit describes detailed protocols for the assessment of phagosome formation and maturation. Particular attention is given to Fc- and complement-receptor mediated phagocytosis, but the protocols provided can be readily adapted to other types of phagocytic processes.