Social Impact Bonds (SIBs) have spread around the globe in the past five years. At a time of pressure on public budgets following the economic crisis, a financing mechanism for social policies that promises to mitigate the public sector risk, increase effectiveness and pay for services now while requiring public contributions later, is likely to attract attention. Few policy tools have been disseminated so far and so fast. Since the first one, which was launched in 2010, 43 SIBs have been set up in 11 countries representing an investment of over 200 million EUR.