Personal but Not Private is about how people put themselves out there on social media despite the challenges of negotiating overlapping and unknown audiences within platforms’ technological, social, economic, and political contexts. Focusing on queer women’s use of mobile apps, the book develops the concept of identity modulation: the processes through which people and platforms modulate—adjust or modify—personal and intimate information. Through qualitative digital and traditional research methods, identity modulation is investigated in queer women’s use of Tinder, a dating and hook-up app; Instagram, a photo- and video-sharing app; and Vine, an app that enjoyed a brief stint of popularity for its short, looping videos. Across these apps, identity modulation involves users and platforms shaping particular dynamics of personal identifiability, reach, and salience in relation to self-representations. Tinder intensifies personal identifiability by importing profile information from other platforms. Instagram and Vine are configured to extend users’ reach through attention-grabbing media formats while Vine, in particular, facilitated salient expressions of sexuality and identity statements. Queer women responded to these affordances, making the apps work for their aims of forming relationships, increasing their social and economic participation, and countering intersecting forms of oppression. However, platform designs, business models, and governance approaches placed limitations on these women’s agency in their identity modulation. These findings point to the need for sociotechnical changes that give individuals greater control over identity modulation as a means to fully realize its world-making potential.