In this paper are reviewed the main reported trends of Al incorporation as a function of the main 4H-SiC epitaxial growth parameters. Al incorporation was found to be limited by its high desorption rate for all the parameters investigated. Due to the lack of a general model describing reasonably the processes of Al incorporation, the concept of surface vacancy induced incorporation was proposed and applied to explain these experimental results. In this model, Al incorporation is mainly driven by the transient formation of Si vacancies at the surface or sub-surface of terraces. It was shown that for increasing Al incorporation, one needs to improve its stability upon adsorption on Si vacancy and/or to reduce its desorption time. In this model, the transient formation of C vacancies at the surface or sub-surface (favored at low C/Si ratio) is proposed to play also a role by destabilizing the incorporated Al atoms.