In biology, cell signaling is part of any communication process that governs basic activities of cells and coordinates multiple-cell actions. The ability of cells to perceive and correctly respond to their microenvironment is the basis of development, tissue repair, and immunity, as well as normal tissue homeostasis. Errors in signaling interactions and cellular information processing may cause diseases such as cancer, autoimmunity, and diabetes. By understanding cell signaling, clinicians may treat diseases more effectively and, theoretically, researchers may develop artificial tissues.

All cells receive and respond to signals from their surroundings. This is accomplished by a variety of signal molecules that are secreted or expressed on the surface of one cell and bind to a receptor expressed by the other cells, thereby integrating and coordinating the function of the many individual cells that make up organisms. Each cell is programmed to respond to specific extracellular signal molecules. Extracellular signaling usually entails the following steps: