Just an FYI: It is always helpful to use the full name and then refer it as an acronym, e.g. Accountable Care Organization, hereafter referred to as an ACO. I say that given I had/have no idea what an ACO is/was.
I Googled it and figured it out. Here is a rather funny video:
http://commonhealth.wbur.org/2010/10/primer-what-is-an-aco-and-why-should-i-care/It is more interesting for the fact that the voices are the same ones used in the Evo vs iPhone wars a few months back without the foul language.