Abstract: The New Public Governance paradigm supports that an interdependent network of public and private institutions, citizens and third sector organizations participate in policy preparation processes and public service delivery. In the last two decades, many initiatives of collaboration and co-production have been carried out to reverse the loss of legitimacy and improve efficiency. However, previous research has shown that these practices may fail to achieve their supposed benefits. This Thesis analyses various public sector innovation initiatives in collaboration and co-production carried out by European and US public sector entities in recent years, in order to measure their degree of adoption, check the achievement of their theoretical benefits and highlight areas for improvement. This study covers initiatives to improve transparency, promote citizens and users¿ engagement, foster public sector innovation processes and improve efficiency. The Thesis has four chapters. The first chapter analyses the adoption and use of Web 2.0 and social media tools by Audit Institutions in the European Union and the United States, at central and regional levels. The second chapter is a case study of the e-participation initiative of the city council of Madrid (Spain), Decide Madrid, to identify the critical success factors and the main barriers that determine its performance. The third chapter analyses users¿ participation in collaborative innovation projects to define their roles in these projects. The fourth chapter analyses the impact of collaborative practices on the efficiency of public service delivery, with a focus on the management of the waste collection service in Spain.