In order to achieve a high level of innovativeness, cities are in collaboration with public and private organisations that allow city halls to tap into networks of companies and clusters as well as execute projects. This article focuses on this kind of public or private firm, public open innovation (POI) intermediaries, which operate in the public sector. An exploratory multi-case study was conducted with the participation of POI intermediaries and local governments in Finland, Germany, the Netherlands and Spain. The eight cases reveal that certain public or private companies act as a bridge - POI intermediary - across the large cognitive distances between city halls and a network of organisations, while orchestrating the collaboration of actors and executing innovation projects. These findings motivate policy makers to enhance the innovativeness and competitiveness of cities, and they offer useful guidelines for city halls to improve their innovation process and remove possible obstacles.