**Abstract**

Decades of observations and theoretical studies present intriguing results about black hole accretions: supermassive black holes (SMBHs), located in the centers of galaxies, are accreting similar to Galactic stellar-mass black hole systems (GBHs). This is the unified model of black hole accretion, which indicates active galactic nuclei (AGNs, the accreting SMBHs) are only the scaled-up version of galactic X-ray binaries (XRBs, the accreting GBHs). The analogy between AGNs and XRBs ensures us to determine AGN evolutions on cosmological timescales by simply studying the quickplaying Galactic systems, which is much easy in observation and modeling. X-ray emission is produced by the inner region of the accretion disk and corona, which is close to the black holes and provides the diagnostics of accretion strength. Meanwhile, radio emission is an indicator of the ejection process, which is another fundamental part of accreting black holes. Furthermore, accreting flows are also regulated by black hole masses and accretion rates/Eddington ratios. Therefore, the unified model of black hole accretion is the correlation between accretion and ejection process and black hole masses. In this chapter, we will review models concerning the unified model of black hole accretions and present recent updates in this area.

**Keywords:** accretion, stellar mass black holes, supermassive black holes, X-ray binaries, active galactic nuclei, jets, accretion disks
