1. Negative screening eliminates companies that do things that you don't like, such as tobacco, human rights violations, pornography, and animal testing.
2. Positive screening supports companies that embody your values and beliefs. That's a little more complicated. Do you choose something that's best in class — even if it's a problematic class? McDonalds is offered as an example held by Amy Domini of Domini Social Investments for that reason. If you're interested in Women's issues, check out The Women's Equity Fund. Portfolio 21 and Sierra Club Funds focus on environmentally progressive companies.

The article mentions that "socially responsible investment has also evolved to include the practice of shareholder advocacy. Some shareholders use their ownership of stock to try to pressure companies to change their behavior."

If you're concerned about climate change, check out Ceres' Resolution Tracker for the 2007 Proxy Season, a one page outline of all climate resolutions filed this season, and exercise your proxy voting power.