During endocytosis, extracellular molecules and plasma membrane components are selectively internalized by cells. This fundamental process of -cellular ingestion- is required for diverse activities such as nutrient uptake, cell adhesion and migration, signal transduction, cytokinesis, neurotransmission, and antigen presentation. Pathogens (e.g., HIV) exploit endocytic pathways to gain entry into cells, and defects in the endocytic machinery can lead to diseases such as cancer. Written and edited by experts in the field, this collection from Cold Spring Harbor Perspectives in Biology covers...