The topic of this book, Collectins, is a family of proteins whose major function is in innate immunity, where Collectins act as pattern recognition receptors (PRRs). In general they recognize targets such as microbial surfaces and apoptotic cells, and once bound to a target, Collectins promote the clearance of microorganisms and damaged host tissue. New cell-surface proteins and glycoproteins, which act as Collectin receptors, are currently being identified. Some Collectins, particularly MBL, activate the complement system, which enhances the ability of antibodies to fight pathogens, via three MBL-associated proteases, the MASPs. Additionally, recent research has begun to show wider-ranging activities of Collectins, such as: