The pious sex. Catholic constructions of masculinity and femininity in B elgium (c. 1800-1940) This study has a double goal. On the one hand it wants to improve the kn owledge of Catholic constructions of masculinity and femininity in Belgi um. On the other hand, by studying these gender constructions, it wants reconsider the feminisation thesis. This thesis has developed in histo rical research into a container term that covers various contents. It po ints not only at a numeric preponderance of women in the religious field , but also at content changes and at a quasi-identification of feminini ty and religiosity. The nineteenth-century feminisation of Christia nity has been studied and documented in various European countries and d enominations, but in the research on Belgian Catholicism it has not yet been a major theme. Still, Belgian society offers an interesting case as the Catholic realm covered a wide range of activities. As such, women a nd men could confirm their Catholic identity in both public and more pri vate fields. This study therefore focuses on the Belgian case, and more specific on the way in which gender differentiation was created and expr essed. Focus is put on the Catholic adult laity and his or her (ideal) i mage in the Sacred Heart devotion, Catholic Action and sermons. These pe rspectives offer the opportunity to point at the diversity and the flexi bility of these gender constructions. The construction of the Catholic m an in the discourse of the Apostolat de la Prière (a devotional movement dedicated to the Sacred Heart) for instance illustrates how masculinit y and emotionality were not necessarily considered mutually exclusive . This nineteenth-century emotionally expressive masculinity therefore m akes it hard to define the nineteenth-century Sacred Heart devotion as feminised on the ground of her emotionality and sentimentality, as has been suggested in other studies. Terms such as feminisation and th e parallel masculinisation not only come close to an essentialist visi on, they also seem to point at a kind of permanent construction of masc ulinity and femininity whereas in current gender research stress is p ut on the historical, social and geographical flexibility of gender cons tructions. Furthermore the stereotype of the pious sex appears to be o lder than the nineteenth century and it was not always used in a positiv e way in Catholic sources of the nineteenth- and twentieth century. The Catholic clergy noted the preponderance of women in religious practices also in the seventeenth century. The clergys observation of mens small er interest in the religious field crystallised into a narrative of loss by the end of the nineteenth century; it incited men-oriented initiativ es and (re)definitions of religion as masculine. Similar initiatives h ave been described in other research as masculinisation, but as indica ted this term is confusing. In order to be able to grasp in historical r esearch this special attention for mens involvement, this study suggest s stepping away from the somewhat confining terms feminisation and masculinisation and put the emphasis on differentiation instead, the crea tion of the difference. This offers the opportunity to describe the incr easing attention for gender difference as can be remarked in the evoluti on of the mixed Apostolat de la Prière movement into the gender-exclusiv e Leagues of the Sacred Heart. Moreover, men do not necessarily have t o oppose women: Catholic men can be compared to other men, e.g. soc ialist men. By shifting the attention towards differentiation, other ca tegories such as class can receive ample attention and e.g. the evolutio n of the originally workers-oriented Leagues of the Sacred Heart can be better defined.