The Ras-superfamily of small G proteins is a family of GTP hydrolases that is regulated by GTP/GDP binding states. One member of the Ras-superfamily, Rab, is involved in the regulation of vesicle trafficking, which is critical to endocytosis, biosynthesis, secretion, cell differentiation and cell growth. The active form of the Rab proteins, which contains GTP, can recruit specific binding partners, such as sorting adaptors, tethering factors, kinases, phosphatases and motor proteins, thereby influencing vesicle formation, transport, and tethering. Many Rab proteins share the same interacting partners and perform unique roles in specific locations. Because functional loss of the Rab pathways has been implicated in a variety of diseases, the Rab GTPase family has been extensively investigated. In this review, we summarize Rab GTPase-mediated membrane trafficking while focusing on the structures of Rab protein and Rab-effector complexes. This review provides detailed information that helps explain how the Rab GTPase family is involved in membrane trafficking.