Extracted 12AUG2011 from http://blogs.hbr.org/hbr/meyer-kirby/2011/08/the-social-impact-bond-as-iron.html
The social impact bond is a new financing approach that lets societies benefit from risk-taking on new ideas for social programs, without asking their governments to foot the bills for experiments that don't pan out. Instead, the risk is born by private investors, often including NGOs...
Clearly, it's not a hot investment arena for speculators hoping to maximize the return on their capital. But for those motivated to use their capital to make the world better, it's a terrific mechanism for driving change at scale.
[brief discussion of the seeds of this funding approach in the 19th Century and speculation about its attractiveness today]