Decidim is a project to build a framework and a digital infrastructure for participatory democracy. Since the end of 2015 we have been practically deepening the relationship between network communication technologies and political participation. Our work on 15M and the use of digital networks for collective action, as well as the development of democratic technologies during the D-CENT project, has helped us to conceive and design prototypes and practices of technologically mediated participation. The Decidim.barcelona platform, designed for the participation process for elaborating the Municipal Action Plan 2016-2019 (PAM), was based on Consul, the software behind the participation platform of the Madrid City Council, Decide Madrid. Later, Decidim has been rewritten from scratch to facilitate a more modular development, a process that has resulted in decidim.org.