This review discusses the role of Rab GTPases in regulating intracellular membrane traffic and cell physiology. Rab proteins act as master regulators, controlling various steps of membrane traffic, from vesicle formation at the donor membrane to fusion at the target membrane. They interact with effector proteins to select cargo, promote vesicle movement, and ensure correct fusion sites. The review highlights how Rab dysfunction leads to diseases ranging from infectious diseases to cancer. It also explores the structural and functional aspects of Rab proteins, including their conserved structure, cycling between active and inactive states, and interactions with regulatory proteins like GDI, REP, GAP, and GEF. Additionally, the review covers the diverse effector proteins that interact with different Rabs, their roles in vesicle formation, movement, tethering, and fusion, and the mechanisms by which Rabs communicate with each other to define organelle identity and establish directionality in membrane traffic.This review discusses the role of Rab GTPases in regulating intracellular membrane traffic and cell physiology. Rab proteins act as master regulators, controlling various steps of membrane traffic, from vesicle formation at the donor membrane to fusion at the target membrane. They interact with effector proteins to select cargo, promote vesicle movement, and ensure correct fusion sites. The review highlights how Rab dysfunction leads to diseases ranging from infectious diseases to cancer. It also explores the structural and functional aspects of Rab proteins, including their conserved structure, cycling between active and inactive states, and interactions with regulatory proteins like GDI, REP, GAP, and GEF. Additionally, the review covers the diverse effector proteins that interact with different Rabs, their roles in vesicle formation, movement, tethering, and fusion, and the mechanisms by which Rabs communicate with each other to define organelle identity and establish directionality in membrane traffic.