Changes in development drive evolution to produce exceptionally diverse morphologies, but too often, there is insufficient knowledge about either a system’s evolutionary history or developmental parameters to link the two together. The malleable fin configurations in the Actinopterygii (ray-finned fish), a clade of over 30,000 species, serve as a riveting case study for the chance to couple evolution and development to explain morphological diversity. Ray-finned fish possess two sets of paired fins, the pectoral and pelvic fins, and three unpaired median fins – the caudal, dorsal, and anal fins. While the positions of the fins, especially the paired fins (or the homologous forelimbs and hindlimbs), is constrained in the rest of jawed vertebrates, fin configuration is remarkably labile in actinopterygians. In this dissertation, I first attempt to characterize the evolutionary patterns of fin positioning in actinopterygians to gain an understanding of which groups were displaying the most pronounced changes, and to obtain a sense of how constrained these fin shifts might be. Next, I investigate zebrafish (Danio rerio) pelvic fin development to determine where the pelvic fin precursor cells arise from. Finally, I present a synthesized view of how developmental changes in actinopterygian fish might have facilitated their diverse fin configurations.