A few months ago I threw together a short presentation on the history of calcium imaging for a journal club here at Janelia. It is incomplete. It lacks notes. It focuses much attention on early genetically-encoded indicators. However, calcium imaging is so intertwined with the work of Roger Tsien, my Ph.D. thesis advisor, and since he just won the Nobel Prize, I thought it might be of some interest to the audience of Brain Windows. It does provide a little bit of background for some of the more recent developments chronicled on this site.