Jets and outflows are generic features of accreting objects. Spectral and morphological similarities in relativistic jets from black holes of stellar mass and from AGNs suggest a fundamental similarity of the jets that stems from the scale invariant nature of strong gravity. Detailed comparison of the nuclear properties of a sample of accreting black holes reveals a strong correlation between the radio emission, the X-ray luminosity, and the black hole mass that can be understood in terms of simple, very generic scaling relations. Using these relations, we can constrain the X-ray emission mechanism, jet speed, and jet power of the sources under consideration.