Autonomous cells are engineered biological systems capable of biosynthesising and directly incorporating non-canonical amino acids (ncAAs) into proteins. These systems have the potential to extend the applicability of the genetic code to enable large-scale fermentative production of proteins carrying ncAAs. This work evaluates approaches for the generation of autonomous and semi-autonomous cells. Semi-autonomous cells rely on the external addition of a precursor, which is enzymatically converted in vivo to an ncAA that is directly incorporated. In contrast, autonomous cells have a metabolic system that produces and directly incorporates an ncAA in vivo. Through a critical evaluation of the state of the art, the reader is provided with an opinion on the future development of the field.