Cells go through a natural life cycle which includes growth, maturity, and death. This natural life cycle is regulated by a number of factors, and the disruption of the cycle is involved in many disease states. For example, cancer cells do not die the way normal cells do at the end of their life cycle. Here we look at the various processes by which cells age and die, both programmed and unprogrammed. Cellular senescence is part of the normal aging of a diploid cell where it loses its ability to divide. Some sources suggest that senescence occurs via programmed gene expression changes, or that it is a result of an accumulation of DNA double strand breaks or toxins. Cellular senescence is easily detected by measuring Senescence Associated ß-galactosidase (SA-ß-gal), a hydrolase enzyme that catalyzes the hydrolysis of ß-galactosidase into monosaccharides only in senescent cells. Programmed cell death happens naturally as a result of a cascade of signals within the cell itself. The most common form of programmed cell death, apoptosis, plays an important role in population control and prevents massive cell growth which could lead to a possible tumor. In embryogenesis, apoptosis allows the digits of our fingers and toes to acquire their normal shape that is instead of having webbed hands and feet. The cell is ultimately triggered to commit suicide when the correct internal signals are activated