Women navigate an unprecedented amount of gender-based harassment in online environments. The breadth of this aggression has received attention not only from academics, but in popular press, where it has been widely critiqued as unfortunate consequences of trolling culture. Largely absent from these conversations is the role of gender, and in particular masculinity, in sustaining harassment in digital contexts. In this talk, I examine the connections between masculinity and sociotechnical affordances of computer-mediated communication in men's motivations to gender harass online. I propose that men's endorsement of online gender-based harassment is motivated by attempts to (re)affirm their masculinity following threats that question their manhood. Anonymity afforded by online communication can exacerbate these effects, since the impression of being anonymous makes it easier to engage in harassment. Technology therefore enables gender harassment to thrive, yet men's motivations to gender harass are grounded in performances of masculinity and maintenance of gender relations between (and among) women and men.