 Stephens' most important work, "The Literature of the Kymry" (1849, 2nd ed.1876), was based on his essay "The Literature of Wales during the Twelfth and Succeeding Centuries" which won the Prince of Wales Prize at the 1848 eisteddfod held in Abergavenny.In this work, Stephens pioneered the use of rigorous methods of literary criticism in the study of medieval Welsh literature.