After falling out of fashion somewhat(Schmitz, 2006) there has been a resurgence of interest inconditional or results-based instruments over the last fewyears. Faced with increasing pressure on budgets andsometimes frustrated with the perceived ineffectiveness ofdevelopment spending, policy makers have started to explorenew ways of structuring development support in order to domore with less. However, as is well known, conditionalityhas a mixed track record. It is therefore important tounderstand where, when, and how these new instruments arebest deployed; what their strengths are, and what theirweaknesses; and what critical information we are stillmissing about them. Initial research on these newinstruments is emerging, but so far there is no overarchingstructure or overall research program that unifies theseefforts. A review that provides a general overview of thisburgeoning field may therefore be useful both to policymakers and to researchers: it can both summarize the currentstate of the art and it may help to prevent duplicateresearch as well as identify gaps that could usefully befilled. This paper conducts such a review and seeks tosummarize the already existing research on this topic. Thereport is structured as follows. First the authors give anoverview of the subject matter, describing the concept andthe terminology of results-based approaches. Next, theysurvey the research landscape on this topic, pointing outwhich areas are well covered, and which ones less so. Insections four and five the authors then structure andsummarize the start of the art in theoretical research(section four) and in empirical research (section five). Theauthors conclude with some overarching findings andquestions for further research.