Planck’s pioneering contributions to special relativity have received less consideration than one might expect in the historiography and philosophy of physics. Although they are celebrated in isolation, they are mostly not understood as integral to an overarching project. This paper aims (a) to provide a historically accurate overview of Planck’s contributions to the early history of relativity that is reasonably accessible to today’s reader, (b) to demonstrate how these contributions can be presented against the background of Planck’s ‘Helmholtzian’ vision of (...) relativistic general dynamics based on the principle of relativity and principle of least action, and (c) to argue that Planck’s general dynamics serves as an illuminating example of the use of ‘principles’ in physics. (shrink)