HEI held a workshop on December 8, 2016, to provide an overview of research on the effects of fuel composition on particulate matter (PM). Introductory presentations included overviews of regulatory issues, of engine/vehicle parameters, and of fuel formulation, as well as tail-pipe emissions versus ambient levels of PM. Other presentations discussed the impact of gasoline composition (including ethanol level and aromatics) and engine technology (including gasoline direct injection) on PM emissions. The workshop page includes presentation slides. A summary is forthcoming.