Mr. Vaessen is CEO at Zimmerman & Zimmerman, an open-source data and visualization company based in Amsterdam, The Netherlands. He serves as technical liaison to the efforts made by Zimmerman & Zimmerman to maintain a sustainable data-engine, enabling organisations like DfiD, UNESCO, Dutch Ministry of Foreign Affairs, UN-Habitat, the Overseas Development Institute and the Dutch Enterprise Agency to build relevant data portals based on the open data format IATI.