Endocytosis has long been thought of as simply a way for cells to internalize nutrients and membrane-associated molecules. But an explosive growth in knowledge has given a new dimension to our understanding of this process. It now seems that endocytosis is a master organizer of signalling circuits, with one of its main roles being the resolution of signals in space and time. Many of the functions of endocytosis that are emerging from recent research cannot yet be reconciled with the canonical view of intracellular trafficking but, instead, point to endocytosis being integrated at a deeper level in the cellular 'master plan' (the cellular network of signalling circuits that lie at the base of the cell's make-up). Deconvolution of this level, which we call the 'endocytic matrix', might uncover a fundamental aspect of how a cell is built.