Accreting supermassive black holes are thought to drive the energy output in the form of radiation and relativistic plasma outflows (jets) seen in Active Galaxies. As such they allow us an excellent opportunity to probe the realm of extreme physics.
I will highlight some recent results on the high-energy diagnostics of these objects, ranging from non-thermal magnetospheric processes in the vicinity of supermassive black holes to the physical characteristics of their large-scale jets.
On black hole horizon scales, gap-type particle acceleration could be responsible for the rapidly variable gamma-ray emission seen by ground-based VHE instrument, and provide the plasma source needed for continuous jet formation. On larger scales, stochastic-shear particle acceleration could be behind the extended high-energy emission seen in their kilo-parsec-scale jets. I will give an introduction to these scenarios, comment on their potential role for UHECR production, and discuss some current caveats and challenges.