This dissertation examines the development of evolution as a cosmic concept—that is, as a concept that people applied to both the physical transformations of the astronomical heavens and to everything else in the universe—across the eight decades preceding Charles Darwin's 'On the Origin of Species' (1859). The story I tell is centered in Britain, but with important roots in, and connections to, French and German natural philosophy. The language people used to refer to the concept of the transformation of organic and inorganic nature changed over the time period in question, of course, but it did so within a consistently universal paradigm that extended a single transformist law or principle to everything in the universe, from the transformation of nebular matter into solar systems, to the development of the earth, to the emergence and transformation of organic life on its surface, the progress of individuals and human societies, and even life in a spiritual world to come. This cosmic evolutionary paradigm was developed in the context of imaginative habits of thought associated with a historical movement known as Romanticism. The story of cosmic evolutionary thought is important for three reasons. First, it reveals the way in which evolution was a feature of nineteenth-century thought more generally, uncovering new avenues for historical research across domains of study. Second, it presents evolution not as the product of a few individual moments of genius, but as a rising tide of thought that saturated literary, religious, social, political, and natural philosophical life. Finally, our understanding of evolution in particular, and the scientific enterprise more generally, are transformed by a clearer recognition of the imaginative, Romantic roots of evolutionary ideas. The story of the cosmic evolutionists demonstrates the critical role of imagination in science, and particularly evolutionary, historical accounts of nature, while also examining the controversy that has accompanied it from the very beginning.