Institute for Advanced Study/Princeton University Joint Astrophysics Colloquium

After 50 years of dreaming about it, space-based microlensing observations are now underway. A 2014 100-hr Spitzer Pilot Program generated "microlens parallaxes" for dozens of lenses, opening the prospect of measuring the Galactic distribution of planets. This program will be expanded 8-fold in 2015. Analogous observations by Kepler will measure the mass function of free-floating planets. WFIRST microlensing observations will, as advertised, "complete the planetary census" but they will do an immense amount of astrophysics as well. I discuss how microlensing's take off builds on rapid, ongoing, ground-based developments.