This article describes some aspects of the history of the discovery of the structure and function of Photosystem I (PS I). PS I is the largest and most complex membrane protein for which detailed structural and functional information is now available. This short historical review cannot cover all the work that has been carried out over more than 50 years, nor provide a deep insight into the structure and function of this protein complex. Instead, this review focuses on more personal views of some of the key discoveries, starting in the 1950s with the discovery of the existence of two photoreactions in oxygenic photosynthesis, and ending with the race towards an atomic structure of PS I.