The purpose of this chapter is to explore the extent of, and limits to, the role investors might play in addressing the harmful social and environmental impacts of the companies in which they invest. Such a focus may give the appearance that I think the glass is half empty; that companies in particular, and capitalism in general, are a source of problems that investors and others must solve. This is not, however, the case. Rather, I believe very strongly that the glass is half full. Companies competing in free markets have a hugely valuable role to play in creating many of the products and services, jobs, tax revenues and investment returns on which modern economies depend. They also have a vital and positive role to play in providing the investment, research and technology necessary to solve our most pressing social and environmental problems - from renewable energy technologies to medicines to treat diseases such as AIDS. Capitalism has many strengths, and investors play a crucial and positive role in providing and efficiently allocating capital.