The environment of the putative massive
black hole in the central engines of AGN is studied by using existing
observations from the entire wavelength
range (radio to 
-rays) as well as performing observations in the
X/ -ray region. Both -ray loud (blazars) and
-ray weak (Quasi-Stellar Objects and Seyfert Galaxies) sources
are studied.
In blazars, the line of sight lies close to the jet axis allowing an unobscured view of the inner jet regions. The modelling of the radio-optical spectral component focuses on the (magnetic) geometry of the inner jet region, on the electron acceleration process, and on the radius-to-frequency mapping of the observed radiation.
In Seyferts,
the line of sight often passes through absorbing gas, e.g. a molecular
torus. The UV to -ray continuum is modelled in order to study the
geometry and physical conditions in the coronal regions of the black
hole accretion disk.