The WFIRST mission will utilize a 2.4 meter telescope with a wide field of view in the infrared to address some of the most compelling problems in astronomy. The mission will produce breakthrough science in a number of areas: (1) its microlensing program should discover ~2000 exoplanets and complete Kepler”Ēs exoplanet census; (2) its coronagraph will characterize the atmospheres of nearby planets; (3) its dark energy program will use multiple tools (supernova, gravitational lensing, large-scale structure) to study the origin of cosmic acceleration; and (4) its hundred-fold increase in field-of-view over Hubble will enable a wide-ranging general observer program. I also briefly discuss Japan”Ēs contribution to exoplanet science through microlensing.