Missions are nested entities involving multiple interventions at different levels and unclear and evolving boundaries, making traditional evaluation approaches ill-suited to capturing their additionality. This paper proposes mission-evaluation processes and tools that are consistent with their specific features. It notably proposes mission criteria related to their different expected systemic effects; a mission theory of action to support a developmental evaluation that tracks the evolution of the mission design and processes; and a monitoring tool to assess and compare mission-readiness levels across missions and at different stages of the mission life cycle.