This document provides an overview of social business models. It discusses Muhammad Yunus' concept of doing everything in reverse to help people. Social businesses are self-sustaining companies that serve society and improve lives while repaying investor's money. They have a quadruple bottom line of people, profit, planet and purpose. Building social business models requires challenging assumptions, finding partners, experimentation, prioritizing social profit, and specifying the social mission to avoid mission drift. The document provides examples and resources for learning more about social enterprises.