CD4+CD25+ regulatory T (Treg) cells play a crucial role in maintaining self-tolerance and preventing autoimmune disease. The transcription factor forkhead box protein 3 (Foxp3) has been identified as a molecular marker for Treg cells. Foxp3 is highly expressed in lymphoid tissue and several signalling pathways influence its expression. It plays an essential role in the development and function of Treg cells. Mutations in Foxp3 are responsible for the scurfy (sf) mutant mouse, and for autoimmune human diseases including the X-linked fatal "immune dysregulation, polyendocrinopathy, enteropathy, X-linked" (IPEX), autoimmune colitis and rheumatoid arthritis. Recent studies have also revealed an important and novel anti-atherogenic role for Treg cells and consequently for Foxp3. These data open up potential novel therapeutic avenues for the management of atherosclerosis.