The Near-Infrared Imager and Slitless Spectrograph (NIRISS) is one of the four JWST science instruments integrated together with the Fine Guidance Sensor (FGS). Both FGS and NIRISS are provided by the Canadian Space Agency. NIRISS is a near-infrared (0.8-5 um) camera featuring four observing modes: imaging, single-object and wide-field slitless spectroscopy and aperture masking interferometry. These observing modes enable a wide variety of science programs, from the study of the early universe to the atmospheric characterization of exoplanets. This talk will present the NIRISS capabilities and an overview of the NIRISS Guaranteed Time Observations program.