The human serpin superfamily consists of at least 35 members that target not only serine proteases, but also selected cysteine proteases and non-protease proteins. Serpins bind the protease active site resulting in a major conformational rearrangement that traps the enzyme in a covalent acyl-enzyme intermediate. As protease inhibitors, serpins have an array of functions including regulating blood clotting, the complement pathway, extracellular matrix remodeling, and cell motility. They are also involved in activities that extend beyond their ability to inhibit proteases. For instance, they may also regulate blood pressure, angiogenesis, or act as storage/transport proteins.