p21^Cip1/Waf1 is a protein that plays a crucial role in regulating the cell cycle. It is part of the Cip/Kip family of cyclin-dependent kinase inhibitors, which means it helps control the activity of enzymes that drive cell division. By inhibiting these enzymes, p21 can prevent cells from progressing through the cell cycle, particularly in response to DNA damage. This protein is also involved in various cellular processes, including apoptosis and DNA repair. Its expression is often induced by p53, a well-known tumor suppressor protein, in response to stress signals. By regulating cell growth and maintaining genomic stability, p21^Cip1/Waf1 contributes to preventing cancer development.