Data obtained at all wavelengths, and in particular at high and very high energies have unveiled astrophysical outflows as very luminous and sometimes rapidly varying sources. The very high luminosities, and particle energies, involved in the emission from galactic microquasars and binary systems with pulsar are a serious challenge for the present models. Massive young stellar objects are turning out to be particle accelerators with potentialities at high energies that start to be considered. Extragalactic jets of active galactic nuclei present very fast and efficient radiation even when their jets do not point towards us, against the common belief that only blazars can be powerful and fast varying sources. Finally, the termination regions of galactic and extragalactic outflows are detected not only in radio, but also in X-rays and even in gamma-rays. In this talk, I will present several scenarios of gamma-ray emission from all these sources, giving a brief overview of several models developed to explain or predict high-energy radiation from outflows or jets at different spatial scales.

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