The plasma proteome is one of the most important proteomes from a diagnostic standpoint, as quantitative changes between normal and diseased states can be used to discover novel biomarkers for clinical diagnosis and therapeutic monitoring of diseases. HUPO’s Plasma Proteome Project has involved characterization of the plasma proteome by an international consortium using technologies ranging from antibody arrays to mass spectrometry and has helped in the construction of a substantial catalog of plasma proteins. Our group has developed the Plasma Proteome Database (http://www.plasmaproteomedatabase.org) as a comprehensive resource of annotated data for posttranslational modifications, single-nucleotide polymorphisms, tissue expression, subcellular localization, and disease involvement of plasma proteins. This database should serve to facilitate further research to help understand the plasma proteome in health and disease.