Mammalian cytochromes P450 have been shown to play highly important roles in the metabolism of drugs and xenobiotics as well as in the biosynthesis of a variety of endogenous compounds, many of them displaying hormonal function. The role of P450s as therapeutic targets is still inadequately recognized although several P450 inhibitors became efficient drugs that even reached blockbuster status. Here, we try to give a comprehensive overview on cytochromes P450s, which are already well-established targets - particularly focussing on the treatment of infectious diseases, metabolic disorders and cancer - and on those, which have a high potential to become successful targets. In addition, the design of inhibitors of cytochromes P450 will be discussed.