The Wide Field Infrared Survey Telescope (WFIRST), which is planned for launch in 2025, is NASA’s next large space observatory after the James Webb Space Telescope. It contains two primary science instruments: A Wide Field Instrument (WFI) to carry out surveys of galaxies in the near infrared; explore the properties of dark energy and dark matter; and carry out a microlensing survey to complete the census of exoplanets, and a Coronagraph Instrument (CGI) to demonstrate high-contrast technology for exoplanet imaging and spectroscopy. Understanding how to implement the technology for CGI is a critical step toward future, larger missions targeted at direct imaging of Earthlike planets in the habitable zone of nearby stars. This paper presents an overview of the current instrument design and requirements, highlighting the critical technologies being demonstrated. These include two types of coronagraphs, closed-loop wavefront control with two deformable mirrors, a visible-light, electron multiplying detector (EMCCD), and a lenslet based integral field spectrograph. Additionally, critical algorithms will be developed and tested for low- and high-order wavefront control, spectral extraction, and post-processing for planet detection. The paper will also describe the operational plans for the instrument. A participating scientist program (PSP) will enable members of the community to engage in the technology demonstration and, if warranted by instrument performance, will incorporate science focusing on imaging and spectra of large Jupiter size planets and protoplanetary and debris disks and a blind search program for undiscovered Jupiters and possibly mini-Neptunes.