How should we "fix" digital technologies to support democracy instead of undermining it? In Designing for Democracy, Jennifer Forestal argues that accurately evaluating the democratic potential of digital spaces means studying how the built environment - a primary component of our "modern public square" - structures our activity, shapes our attitudes, and supports the kinds of relationships and behaviors democracy requires. While many scholars and practitioners are attentive to the role of design in shaping behavior, they have yet to fully engage with the question of what structures are required to support democratic communities - and how to build them. Forestal closes this gap by providing a new theory of democratic space. Drawing from a wide range of disciplines, including architecture, psychology, and the history of political thought, she argues that "democratic spaces" must be designed with three environmental characteristics - boundaries, durability, and flexibility - that, taken together, afford users the ability to engage in fundamental civic practices. Through extended analyses of Facebook, Twitter, and Reddit, Forestal shows precisely how well these digital platforms meet the criteria for democratic spaces, or whether they do so at all. The result is a more nuanced analysis of the democratic communities that form - or fail to emerge - in these spaces, as well as more concrete suggestions for how to improve them. In connecting the built environment, digital technologies, and democratic theory, Designing for Democracy provides blueprints for democracy in a digital age.