We examine the evolution of the form of the first movement in the eighteenth-century concerto from the Baroque ritornello plan to the eighteenth-century Classical concerto by means of a statistical corpus study. Our data yields a more nuanced understanding of several key characteristics of this evolution, characteristics that have been observed by both contemporary and present-day theorists. We demonstrate how the rise in both quantity and thematic quality of the soloist’s part enabled the convergence of ritornello practices with sonata-form features. We conclude with analytical case studies of works by C. P. E. Bach and Josef Mysliveček, showing how their formal solutions fit within this evolutionary process.