Studies of active galactic nuclei with the VLT interferometer

The observation of extragalactic targets is the most challenging program for interferometric instruments operating at infrared wavelengths. Of them, only the nearest active galactic nuclei (AGN) are bright enough to be reached with the current instruments at the VLT Interferometer (VLTI). So far, two Seyfert galaxies, NGC 1068 and the Circinus galaxy, have been studied in detail with the MID-infrared interferometric instrument (MIDI). First results could also be obtained for the nearby radio galaxy Centaurus A. This lecture gives an account of the current state-of-the art: after spelling out the scientific questions, the investigations of the dust tori in NGC 1068 and Circinus are used to demonstrate the observational challenge and the achieved data quality. The results of these studies provide new astrophysical insights and their comparison with newly developed models of dust tori allows a better understanding the identified structures. Finally, the prospects for extending this kind of studies to more distant and fainter AGN with current and next-generation VLTI instruments are discussed.