Exoplanet Occurrence Rates from Microlensing Surveys

The number of exoplanets detected using gravitational microlensing technique is currently larger than 200, which enables population studies. Microlensing is uniquely sensitive to low-mass planets orbiting at separations of several astronomical units, a parameter space that is not accessible to other planet-detection techniques, as well as free-floating planets, not orbiting around any star. This chapter presents the state-of-the-art knowledge on the demographics of exoplanets detected with microlensing, with a particular emphasis on their occurrence rates. The article also summarizes the current knowledge about free-floating planets, an elusive population of objects that seem to be more common than ordinary, gravitationally bound exoplanets.