Cell signaling allows communication between cells. Information is transmitted in the form of signals by connecting all parts of complex organisms into a functional whole. Signaling allows cells to determine their position and function in the body. Signal molecules bind to receptors on the cell surface and trigger a series of intracellular changes, which control all aspects of cellular behavior, from cell formation to programmed cell death (apoptosis). Disruption of signal transmission between cells will prevent their harmonious activity, and this will result in the appearance of disease. The study of the mechanisms by which healthy cells transmit signals is the basis for understanding the changes in signaling that occur during disease onset. Therefore, knowledge of signal transduction mechanisms helps in finding effective therapies and new medications. Interest in cellular signaling is also related to the fact that many cancers are the result of disruption of signaling pathways that monitor normal cell proliferation and survival.