The Complement FactsBook contains entries on all components of the Complement System, including C1q and Lectins, C3 Family, Serine Proteases, Serum Regulators of Complement Activation, Cell Surface Proteins, and Terminal Pathway Proteins. Domain Structure diagrams are incorporated to clearly illustrate the relationships between all the complement proteins, both within families and between families. The FactsBook also includes the cDNA sequences, marked with intron/exon boundaries, which will facilitate genetic studies.