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The Wide Field Infrared Survey Telescope (WFIRST) is a NASA space observatory designed to address key questions about the Universe and the population of extrasolar planets in our Galaxy. WFIRST is planned for launch in the mid-2020s. One of the main WFIRST science program is a statistical census of exoplanets with a microlensing survey, using about one quarter of the overall observing time. Specifically, the microlensing campaign is expected to be sensitive to detect low-mass planets at orbital separation greater than about 1 AU and to free-floating planets down to the mass of Mars. I am going to introduce the science case of microlensing exoplanets and the WFIRST mission. I will describe the expected yield of the WFIRST microlensing survey and I will report on the main outcomes of some of the current observational programs preliminary to the WFIRST mission. Finally, I will outline the possible role of the VST during the WFIRST microlensing survey.&nbsp

The Wide Field Infrared Survey Telescope (WFIRST) was the top ranked large space mission in the 2010 New Worlds, New Horizons decadal survey, and it was formed by merging the science programs of 3 different mission concepts, including the Microlensing Planet Finder (MPF) concept (Bennett \etal\ 2010). The WFIRST science program (Spergel \etal\ 2015) consists of a general observer program, a wavefront controlled technology program, and two targeted science programs: a program to study dark energy, and a statistical census of exoplanets with a microlensing survey, which uses nearly one quarter of WFIRST's observing time in the current design reference mission. The New Worlds, New Horizons (decadal survey) midterm assessment summarizes the science case for the WFIRST exoplanet microlensing survey with this statement: "WFIRST's microlensing census of planets beyond 1 AU will perfectly complement Kepler's census of compact systems, and WFIRST will also be able to detect free-floating planets unbound from their parent stars\rlap.", Comment: White paper submitted to the National Academy Committee on an Exoplanet Science Strategy; 6 pages (typo fixed)

The Wide Field Infrared Survey Telescope (WFIRST) is a 2.4m space telescope with a 0.281 deg^2 field of view for near-IR imaging and slitless spectroscopy and a coronagraph designed for > 10^8 starlight suppresion. As background information for Astro2020 white papers, this article summarizes the current design and anticipated performance of WFIRST. While WFIRST does not have the UV imaging/spectroscopic capabilities of the Hubble Space Telescope, for wide field near-IR surveys WFIRST is hundreds of times more efficient. Some of the most ambitious multi-cycle HST Treasury programs could be executed as routine General Observer (GO) programs on WFIRST. The large area and time-domain surveys planned for the cosmology and exoplanet microlensing programs will produce extraordinarily rich data sets that enable an enormous range of Archival Research (AR) investigations. Requirements for the coronagraph are defined based on its status as a technology demonstration, but its expected performance will enable unprecedented observations of nearby giant exoplanets and circumstellar disks. WFIRST is currently in the Preliminary Design and Technology Completion phase (Phase B), on schedule for launch in 2025, with several of its critical components already in production., 14 pages, 3 figures, 2 tables