Cross-sector collaborations that engage philanthropy are key to advancing sustainable, resilient and inclusive growth in transatlantic cities of all types. Yet, effective and innovative partnerships that lead to transformative change are still too scarce and can seem undefined or vague. GMF and the European Foundation Centre (EFC) were pleased to have the opportunity to convene a group of transatlantic stakeholders to further develop the ideas and concepts on how to make cross-sector partnerships more effective and transformative in advancing sustainability, resiliency, and inclusive growth in cities of all types. The workshop in Brussels built upon the work that was initiated at the Funder’s Forum on Sustainable Cities (FFSC) workshop in Copenhagen (October 2017), which focused on the challenges and opportunities for cross-sector partnerships, and the ensuing breakout session at BUILD 2017 in Detroit (November 2017), which started to brainstorm and design processes, tools, and structures for better cross-sector partnerships. The workshop brought together the FFSC and BUILD network members who participated in the prior workshops. They prioritized the processes, structures, and tools ideated at BUILD, in terms of what a group such as this can advance in theory and in practice in an innovative and effective way. The group developed the ideas to the point where these were pitched to the rest of the group before exploring how these ideas could eventually be adopted or implemented on the ground.