Near-infrared interferometry is a unique tool to study the inner sub-parsec structure of AGN which is inaccessible with current single dish telescopes. With VLTI/GRAVITY, we can now spatially resolve not just the hot dust continuum on milliarcsecond scales through imaging but also the broad-line region on microarcsecond scales through spectro-astrometry. In this colloquium, I will first review the latest results from our observations of local AGN with GRAVITY where we have mapped the kinematics of the BLR in 7 nearby AGN, measured sizes of the hot dust for 17 AGN, and reconstructed images for two AGN. BLR kinematics have allowed us to independently measure the BLR size and supermassive black hole mass where we begin to find a departure from the radius-luminosity (R-L) relation at high luminosity. I will then discuss our new results at high redshift where GRAVITY+, with the addition of wide-angle off-axis fringe tracking and improved adaptive optics, has allowed for dynamical mass measurements of black holes out to z=4. We find more evidence for the departure from the standard R-L relation at high luminosity and consequently smaller black holes in these super-Eddington quasars. Further, with complementary ALMA and NOEMA observations, these unique quasars have overmassive black holes when compared to estimates of their host galaxy mass. I will end with an outlook to the future, including both the ELT and a next generation interferometer.
