The formation of placenta can be viewed as a controlled process of inflammation or cancer development in which cell proliferation, invasion, and immune surveillance or evasion are promoted in a time- and space-specific manner. This suggests that the functions of prostasin are mainly active in pathophysiological conditions, more so than those in basic or normal physiological conditions. The uniqueness of the prostasin serine protease is its membrane anchorage via a glycosylphosphatidylinositol moiety. This anchorage exposes the entire prostasin molecule to the outside while still being immobilized on the cell membrane and gives prostasin a better chance to be used as a biomarker or drug target. As presented in placenta development, the equilibrium between growth and differentiation dictates healthy and disease states.This book provides readers with an integrated knowledge on serine protease prostasin, starting with its discovery, protein isolation, cDNA, and gene cloning, to its functio