  Fabry-Perot interferometers have advantages over slit spectrographs because
they allow fast narrow-band imaging and post-factum image reconstruction of
spectropolarimetric data. Temperature, plasma velocity, and magnetic field maps
can be derived from inversions of photospheric and chromospheric spectral
lines, thus, advancing our understanding of the dynamic Sun and its magnetic
fields at the smallest spatial scales. The GREGOR Fabry-Perot Interferometer
(GFPI) is one of two firstlight instruments of the 1.5-meter GREGOR solar
telescope, which is currently being commissioned at the Observatorio del Teide,
Tenerife, Spain. The GFPI operates close to the diffraction limit of GREGOR,
thus, providing access to fine structures as small as 60 km on the solar
surface. The field-of-view of 52"x 40" is sufficiently large to cover
significant portions of active regions. The GFPI is a tuneable dual-etalon
system in a collimated mounting. Equipped with a full-Stokes polarimeter, it
records spectropolarimetric data with a spectral resolution of R = 250,000 over
the wavelength range from 530-860 nm. Large-format, high-cadence CCD detectors
with powerful computer hard- and software facilitate scanning of spectral lines
in time spans corresponding to the evolution time-scale of solar features. We
present the main characteristics of the GFPI including the latest developments
in software, mechanical mounts, and optics.
