This chapter explores the practices and problems emerging from experimenting an alternative form of city making: collaborative infrastructuring. It discusses the several key issues in attempting a new city making mechanism, including experiments, collaboration and infrastructuring. The chapter draws on, but differentiates, two approaches to experiments in cities. Urban experimentation is concerned with the political economy of knowledge production as selective parts of a city are transformed into ‘living labs’. Public experimentation focuses on public participation in civic or bottom-up initiatives as practices for speculating and enacting futures. The chapter demonstrates how value, trust and responsibility in collaborative infrastructuring materialise and are also contested in practical arrangements. It also discusses the complex enactments of values, futures and urban governance with the case study of Dublin City Council (DCC) Beta and its ‘Traffic Light Box Artworks’ project. DCC Beta is an initiative led by City Architects, a division of the city council responsible for architectural and urban design.