The chapter explores the emerging paradigm of Open Source Urban Governance, a new urban policy model associated with the extensive use of computer-mediated communication and with the use of different modes of citizen mass collaboration – Crowdsourcing, Neogeography, Volunteered Geographic Information (VGI), and Citizen Science. The chapter is organized into five main sections. The first section discusses the concept of e-participation. The next two sections address the objectives, context, determinants, and ethical issues in e-participation, and the different levels of e-participation in each policy stage and by stakeholder. The last two sections explore the e-tools available for citizen participation in urban governance and the impacts and benefits of e-participation. The chapter ends with a reference to future research directions in this field.