In the debate about smart cities, an alternative to a dominant top-down, tech-driven solutionist approach has arisen in examples of ‘civic hacking’. Hacking here refers to the playful, exploratory, collaborative and sometimes transgressive modes of operation found in various hacker cultures, this time constructively applied in the context of civics. It suggests a novel logic to organise urban society through social and digital media platforms, moving away from centralised urban planning towards a more inclusive process of city-making, creating new types of public spaces. This book takes this urban imaginary of a hackable city seriously, using hacking as a lens to explore examples of collaborative city-making enabled by digital media technologies. Five different perspectives are discussed. Hacking can be understood as (1) an ethos, a particular articulation of citizenship in the network era; (2) as a set of iterative and collaborative city-making practices, bringing out new roles and relations between citizens, (design) professionals and institutional actors; (3) a set of affordances of institutional structures that allow or discourage their appropriation; (4) a critical lens to bring in notions of democratic governance, power struggles and conflict of interests into the debate on collaborative city-making; and (5) a point of departure for action research. After a discussion of these themes, the various chapters in the book are briefly introduced. Taken together they contribute to a wider debate about practices of technology-enabled collaborative city-making, and the question how city hacking may mature from the tactical level of smart and often playful interventions to a strategic level of enduring impact.