Rab GTPases control intracellular membrane traffic by recruiting specific effector proteins to restricted membranes in a GTP-dependent manner. In this Cell Science at a Glance and the accompanying poster, we highlight the regulation of Rab GTPases by proteins that control their membrane association and activation state, and provide an overview of the cellular processes that are regulated by Rab GTPases and their effectors, including protein sorting, vesicle motility and vesicle tethering. We also discuss the physiological importance of Rab GTPases and provide examples of diseases caused by their dysfunctions.