This dissertation examines nature and the supernatural in medieval romance, specifically how romance motifs were transmitted and incorporated into translated and original Middle English romances and Old Norse-Icelandic romances and legendary sagas. These romance motifs include those which entered Middle English and Old Norse-Icelandic literature from French sources, including the romance garden and the forest of aventure, but also those with roots in non-romance sources, like the werewolf and the Loathly Lady. Very few scholars have compared how English and Scandinavian authors evolved during the thirteenth through fifteenth centuries, a period in which both cultures were engaging with the same romance materials. By focusing on cultural inflections of the natural and supernatural in romance, this dissertation opens new avenues of research comparing literary development in later medieval England and Scandinavia. It considers why authors might incorporate non-native literary traditions into their narratives and how conceptions of nature, ecology, and landscape change through the process of transmission and adaptation. The dissertation is divided into four studies on different landscapes and beings common to medieval romance: the garden, the forest, the supernatural mistress, and the so-called "Saracen" giant. The medieval texts analyzed here depict interactions between humans, animals, and supernatural agents in specific environments, revealing medieval conceptions of nature but also manifesting constructs of gender, sexuality, and race. Such comparisons uncover shared attitudes towards nature and the supernatural as entities beyond human control in the literatures of the North Sea cultural zone.