Active galactic nuclei (AGN) are among the most powerful sources of
radiation in the universe. As far as we understand today, their source
of energy is accretion of matter into supermassive black holes with
millions to billions of solar masses. AGN and their most prominent
features - jets - are easy to observe in radio. I present results of a
long-term monitoring program of luminous AGN covering timelines of 14
years. We find strong variability even on timescales of many years.
From the emission statistics we conclude that the properties of AGN
emission are more complex than commonly assumed.