Many of the problems that face policy-makers are complex. Implementation must often contend with interlinked problems, navigate non-linear and unpredictable change processes, and engage a diverse range of stakeholders.

This Briefing Paper builds on ODI research over three years to review the implications of complexity for policy and programme implementation. It has three aims: to give readers the tools to decide when a problem is complex, outline why this matters, and provide guidance on how to achieve results in the face of complexity.

There is a growing collection of models, tools and approaches to intervene effectively in the face of these so-called ‘wicked’ problems to help implementers deal with the challenges more systematically, explicitly and rationally.

However, attempting to address complexity is a double-edged sword. On the one hand there are tools to use and growing legitimacy for approaches not previously seen as ‘scientific’ or ‘rigorous’. On the other hand, it means giving visibility to some practices that were once hidden from sight. Actors will find themselves held accountable for aspects of their work that used to slip beneath the radar, such as the political and relational challenges of implementation. This may be an uncomfortable transition. However, it is essential in order to ensure the effective implementation of policies and programmes.