It is frequently said that the field of mechanics in the ancient world can be neatly divided into the theoretical and the practical. However, the division between these two aspects of mechanics is heavily influenced by our own modern conception of the field. This thesis explores both the nature of theoretical mechanics in the ancient world, and the extent to which it can be considered a distinct field in the available textual evidence. The scope, nature and perception of mechanics in a variety of sources are explored in the initial chapters. The rest of the thesis then examines those sources which seem to provide the most significant content on theoretical mechanics, namely, the Pseudo-Aristotelean Mechanica, Archimedes’ De Planorum Aequilibris, Heron’s Mechanica, and the final book of Pappus’ Synagoge. The primary focus of this investigation being the specific mechanical theories that each of these texts propose and explore.