In the period between c. 1200-1450, a number of pious laywomen from all over Europe acquired reputations for being living saints. Based on the biographies written by their male clerical supporters, the most significant tokens that allowed people to recognize the sanctity of these women were their somatic devotional behaviour, their excessive penitential practices and their reception of divine visions. As many of these mulieres religiosae, or ‘holy women’, gained religious and even political influence within and sometimes beyond their local communities, the clerical opposition to them increased. St. Birgitta of Sweden (1302/03-73) is an example of a highly influential holy woman of the later Middle Ages who met with great resistance in life as well as after. In this paper I would like to put into focus a particular form of canonization, namely the formal legal process for establishing a person’s sanctity which developed in the twelfth century, and investigate how the criteria for female holiness transformed during the period in question. In particular, I shall focus on the canonization process of St. Birgitta, which allows us to see how these criteria were continuously negotiated by the women themselves, their supporters and their opponents.