The Bible requires Jews to tie a tekhelet (blue) cord as part of their tzitzit (fringes on traditional prayer shawl and everyday undergarment). Rabbinic sources of antiquity insisted that the tekhelet dye must have been produced from a marine mollusk termed hillazon. For various reasons, the custom of having this tekhelet cord, which is usually associated with the colors blue or violet, disappeared from Jewish material culture sometime in late antiquity. During the 1880s the Hasidic leader Gershon Hanoch Leiner of Radzin (Radzyn Podlaski, Poland) announced that he had found the ancient hillazon and succeeded in producing tekhelet, which he distributed to his followers. However, his tekhelet did not gain popularity. A much wider interest in tekhelet began in the 1980s, when a new tekhelet was introduced by religious Zionist Jews, resulting in an abundance of Orthodox publications on the subject. However, the 1980s renaissance of tekhelet raised objections from various Jewish Orthodox circles. This paper aims to sketch a preliminary map of the tekhelet debate that took place after the introduction of the second tekhelet in the 1980s. It opens with a brief history of tekhelet, followed by a description of the dominant narrative of contemporary tekhelet, and its main opponents. The rest of the article presents central focal points of the controversy: debates regarding the production of the dye; issues of authority regarding acceptance of the new tekhelet; and a messianic tension revealed by the discussion of tekhelet. By providing a non-Orthodox account of the tekhelet debate, this article sheds light on contemporary tekhelet discourse yet also exposes fundamental issues in contemporary Orthodox Judaism, particularly with respect to the relationship between religion and science, and the tension between radicalism and conservatism.