The past year has been significant advances in the understanding of the structure and function of photosystem I (PS I). The highlights included significant progress in discovering the arrangement and function of subunits of PS I, and improvement of the structure of PS I to 4 degrees resolution, as well as new evidence for the mechanism of the interaction of PS I with its soluble electron carriers plastocyanine, cytochrome c6 and ferredoxin. Substantial progress has been made towards understanding the mechanism of energy transfer from the antenna system to the reaction centre, and the electronic structure of the electron carriers.