The first "XFELO Science Workshop" (see https://portal.slac.stanford.edu/sites/conf_public/xfelo2016 for full list of participants and scientific program) was held at SLAC National Accelerator Laboratory, Menlo Park, CA, from June 29 to July 1, 2016. The main purpose was the discussion of scientific opportunities an XFELO extension of the LCLS-II complex in the future would enable. Chaired by Jerry Hastings (SLAC), it brought together more than 40 researchers from institutes around the world.