This chapter concentrates on the politics of women’s cross-dressing in the nineteenth century. It focuses on Concepción Arenal and argues that her cross-dressing was a form of public activism. She aimed to bring social change with her writings and with direct interventions, of which cross-dressing was a fundamental piece. I discuss the scholarship on Arenal’s cross-dressing and argue that contrary to what has been said, it was related to gender fluidity and not sex. Her wearing men’s clothing served a purpose which I believe calls for a better conceptualization of her activism. The complexity of this type of activism allows us to further understand the fight for women’s intellectual participation, as women, in socio-political debates. Arenal wanted women to be able to take on other functions than those usually ascribed to them and she defended women’s education and their intellectual abilities. Her demands were public and should be called activism. Cross-dressing in this context became a tool for activism.