1.1 AIM OF THIS HANDBOOK 'Wouldn't it be good if we knew what works in innovation policy, to inform future policy making and be more efficient and effective in designing future innovation policy instruments as a result?' This earnest request was made recently by a senior UK politician. Yet, in the last 20 years, hundreds of evaluations and academic studies have been conducted on a wide variety of interventions that, by various means, have an impact on innovation input, output, processes, practices and capabilities. So why is there still uncertainty about this area and what does this new volume add to our understanding of the impacts of innovation policy? Previous studies have mainly focused on specific policies, programmes and projects-to assess their past performance and, in some cases, to improve their future design and implementation. The editors and authors of this book have themselves performed numerous evaluations, and have also tried to learn from existing evaluation evidence. Over the years, however, we have realised that, in the policy making community, learning from existing evidence has its limits. It can often be introspective, drawing lessons from one's own activities and evaluations or from a limited number of narratives labelled as 'best cases'. Less common in the academic and policy making communities are systematic attempts to take advantage of the numerous existing evaluations of innovation policy instruments. Furthermore, academic studies tend to highlight the specific contribution that their method or data makes, rather than producing systematic comparisons or syntheses of the effects of policy instruments. For these reasons the idea of a structured effort to learn from the extensive array of evidence on innovation policy impact both fills a gap and offers promising opportunities for new insights. Supported by Nesta, 1 an international team of innovation policy experts, led by the editors of this book, turned our politician's request into something tangible. Between 2011 and 2013, we conducted a study to gather and synthesise the most relevant and recent evidence on the impact of innovation policy measures. The study was titled the Compendium of Evidence on the Effectiveness of Innovation Policy. 2 This Handbook presents the result of that study. In line with practice in the international evaluation and academic literature, in this Handbook we use the terms policy 'instrument', 'intervention' and 'measure' interchangeably.