Background: Addressing today’s sustainability challenges requires adopting a systemic approach where social and ecological systems are treated as integrated social-ecological systems. Such systems are complex, and the international development sector increasingly recognises the need to account for the complexity of the systems that they seek to transform.

Purpose: This paper sketches out the elements of a complexity- aware monitoring and evaluation (M&E) system for international development programmes in the area of sustainable development.

Setting: Not applicable.

Data Collection and Analysis: The authors draw on existing literature on complexity and evaluation and on their own experience from working in the field of M&E.

Findings: An M&E system should not be seen simply as a tool to track compliance against a pre-determined theory of change. Instead, it is most useful as a real-time approach, constantly defining and re-defining narratives for change that help push systems along trajectories of interest. Dealing with complexity involves embracing uncertainty; and this challenges established notions of accountability—something which funders and implementers must begin to redefine together.

Keywords: monitoring; evaluation; complexity; social-ecological systems; international development programmes; narratives for change; theory of change