Regulation of the water permeability of the apical plasma membrane in collecting duct principal cells is essential for the regulation of renal water excretion, and thus, the regulation of body water balance. The water permeability is partly regulated by trafficking of aquaporin (AQP2) containing vesicles between an intracellular reservoir and the apical plasma membrane. Insertion of AQP2 molecules in the apical plasma membrane is induced by vasopressin binding to the V2-receptor at the basolateral side of principal cells. This activates G-proteins, which stimulate adenylyl cyclase resulting in increased intracellular cAMP-concentration and activation of Protein Kinase A (PKA). AQP2 contains a PKA consensus site at ser256, and phosphorylation of this serine in three out of four AQP2-molecules in an AQP2 homotetramer is involved in the regulated translocation of AQP2 to the apical plasma membrane. The elements of this cAMP mediated pathway, including the possible role of scaffolding A Kinase Anchoring Proteins (AKAPs), is still a major area of research. However, a number of other pathways, many of which are believed to relate to changes in the cortical actin network of the principal cells, are activated during vasopressin induced AQP2-trafficking. The purpose of this review is to present an overview of the currently known cellular signalling pathways and molecular mechanisms involved in controlling the abundance of AQP2 molecules in the apical plasma membrane according to the physiological needs of the body.