The highly co-ordinated movement of the thousands of distinct membrane proteins between the cell surface and intracellular compartments is a critical factor in health and disease. This movement controls the organisation of cells in tissues and communication between cells and their environment. The success of this process depends on the regulated sorting and trafficking of proteins within the highly dynamic endosomal compartments of the cell in processes that are emerging as important drivers of neurodegenerative disease, cancer and metabolic pathologies. An understanding of how endosomal traffic is regulated, and how lysosomal traffic and degradation are modulated, is critical for providing insights into disease and devising new therapeutic approaches.