This paper argues that trust cannot be taken for granted in long-term participatory research and promotes greater consideration to conceptualizing the trusting process as fluid and fragile. This awareness by researchers can reveal to them how the passing of time shapes and reshapes the nature of trusting relationships and their constant negotiation and re-negotiation. The paper draws together literature from different disciplines on the themes of trust, temporality and participatory research and outcomes from interviews and workshops undertaken for The Trust Map project to focus on two key moments that reveal the fragility of trust. These are 1) the subtlety of disruption and trust on trial and 2) trust at a distance. We discuss how trust was built over time through processes of interaction that were continually tested, incremental and participatory.