The GREGOR Fabry-Pérot Interferometer (GFPI) is one of the first-light post-focus instruments for the German 1.5-meter GREGOR solar telescope at the Observatorio del Teide. The GFPI is a tunable dual-etalon system in collimated mounting that allows fast narrow-band imaging. It is designed for spectrometric and spectropolarimetric observations between 530-860 nm and 580-660 nm, respectively, and has a theoretical spectral resolution of about 250,000. The field-of-view in spectroscopic mode is 50" x 38" (25" x 38" in case of Stokes-vector spectropolarimetry). In combination with post-facto image reconstruction it has the potential for discovery science concerning the dynamic Sun and its magnetic field at spatial scales down to about 50 km. The instrument underwent an extended commissioning in 2011 and careful science verification throughout 2012. In this talk I will summarize the main characteristics of the GFPI and present results from both the science verification and first observational campaigns. In addition, I will layout the design of the planned BLue Imaging Solar Spectrometer (BLISS), a second Fabry-Pérot Interferometer for the wavelength range 380-530 nm. I will discuss how both the GFPI and BLISS can be used to extend our knowledge on the structure of sunspots and the solar chromosphere by presenting details to the current state of knowledge on these two topics and by outlining possible improvements.