Originally published in 1904, Whittaker’s A Treatise on the Analytical Dynamics of Particles and Rigid Bodies soon became a classic of the subject and has remained in print for most of these 108 years. In this paper, we follow the book as it develops from a report that Whittaker wrote for the British Society for the Advancement of Science to its influence on Dirac’s version of quantum mechanics in the 1920s and beyond.