The light-gathering capacity and resolving power of the 1.5-meter aperture GREGOR telescope will provide solar observations of the full Stokes vector with high temporal, spectral and spatial resolution. As one of the first-light instruments, the GREGOR Fabry-Perot Interferometer (GFPI) is well suited for observations with adaptive optics (AO) correction. Post-facto image correction (speckle masking imaging and deconvolution) will further enhance the data quality to approach the diffraction-limited resolution of the telescope. We will describe the GFPI optical design and its basic operating procedures. Instruments characteristics such as field-of-view, cadence, spectral resolution, and spectroscopic/polarimetric observing modes will result in boundary conditions, which have to be carefully considered in optimizing the scientific outcome of the first-light observations. We will present two science cases for quiet Sun and active region studies to illustrate the capabilities of this imaging spectro-polarimeter.