Procedures that allow the fractionation of a native Photosystem I complex (PSI-200) into several chlorophyll-containing complexes are now available. Two complexes, each containing ∼50% of the total chlorophyll of the photosystem, can be isolated. One complex contains both chlorophyll a and b and serves as antenna complex for the reaction center while the reaction center complex contains 100 Chl a molecules per P700 and has 7 different polypeptides. Only two of the latter (62 and 58 kDa) contain chlorophyll a and these can be isolated as the photochemically active CPI complex. Based on these fractionation methods, a model that describes the overall organization of the chlorophyll in Photosystem is presented.