This article will review the principal Marian feasts in calendars and offices in use in the Crown of Aragon between the 13th and 15th centuries. It will do so after building a corpus of manuscript and incunable liturgies, held in public libraries and Cathedral archives, examined and transcribed over a period of twenty years. Its objective is to trace the development of the Conception feast in the Crown of Aragon between the 13th and 15th centuries, placing its relative importance as a major or minor feast in contrast with other Marian feasts. Because the Conception feast was introduced during the Middle Ages on 8 December, it merits particular attention and will be distinguished from the Expectation or December Annunciation feast, also called the Conception feast (18 December), with which there is often confusion. In the first part of the article, the Conception feast in its variants celebrated in the dioceses will be examined. In a second part of the article the Conception feast as celebrated by the religious Orders will be examined.