People who wanted to solve a social problem -- like lack of access to clean water or inadequate housing for the poor -- used to create a charity. Today, many start a company instead. Experts concede that not all social problems respond well to the for-profit model. "If you set it up as a business, you might be able to raise money more quickly and grow more quickly," says David Bornstein, the author of "How to Change the World," an often-cited book on social entrepreneurship. "But if you want to be profitable, you might find that you have to make choices that diminish the quality of your program," Mr. Bornstein said. It often comes down to one crucial question: "As you grow, will the economics of your business work in favor of your mission or will they work against it?"
