Boundary spanners and boundary spanning activities have been established as key to enabling cross-sector collaboration. By means of a longitudinal study and a process approach to collaboration, the paper offers a novel perspective on interrelated acts of sensemaking and framing whereby boundary spanners representing different organisations and sectors deal with organisational and institutional differences when collaborating. The study focuses on Crossroads, an initiative aimed at addressing an emerging societal problem through cross-sector collaboration including the establishment of a Civil Society Public Partnership (CSPP). To establish and develop the CSPP, multiple boundary spanners representing different organisations and roles interact in a process of continuous negotiation of frames and meaning. The paper elucidates the implications of successive boundary spanning in cross-sector collaboration by highlighting the importance of reticulism, interactive framing, shared commitment, reflexivity, and adaptability.