Participatory urban planning is considered an important aspect of developing local democracy. Recently, the use of mobile technologies to engage with citizens has gained interest among researchers, policy-makers, and activists. The purpose of this article is to introduce a typology that identifies types of mobile applications (apps) supporting citizen participation in urban planning. The presented typology is developed based on theories of participation and has three dimensions: type of data collected, information flow, and empowerment of citizens. Overall, the typology identifies eight types of participatory apps. Participatory apps in use around the world are then plotted into the typology and their contribution is analyzed with reference to the dimensions of the typology. Apps evolve from sharing information on the surrounding environment towards a dialogue aimed to accommodate citizen knowledge into the planning process. The article concludes that the impact of planning apps has yet been modest, but is expected to increase, and discusses ways in which planning apps can leverage citizens' knowledge in the future.