The idea that technology is an extension of the human organism is encountered regularly in the history of thought about technology. The idea, in its most basic form, is that technical objects extend the human organism by replicating or amplifying bodily and mental abilities. This idea is usually presented as a key to a better understanding of technology. In this essay, I will discuss three theories of technology as extension, as developed in book-length studies by Marshall McLuhan, Ernst Kapp, and David Rothenberg. My aim is to investigate whether there is a valid and useful sense of extension according to which technology can indeed be analyzed as an extension of human faculties or organs. The outcome of this investigation will be affirmative, and I will end up presenting a unified account of technology as extension of human faculties, that builds on previous accounts.