Most of us want to make a difference. We donate our time and money to charities and causes we deem worthy, choose careers we consider meaningful, and patronize businesses and buy products we believe make the world a better place. Unfortunately, we often base these decisions on assumptions and emotions rather than facts. As a result, even our best intentions often lead to ineffective-and sometimes downright harmful-outcomes. How can we do better?

While a researcher at Oxford, trying to figure out which career would allow him to have the greatest impact, William MacAskill confronted this problem head on. He discovered that much of the potential for change was being squandered by lack of information, bad data, and our own prejudice. As an antidote, he and his colleagues developed effective altruism, a practical, data-driven approach that allows each of us to make a tremendous difference regardless of our resources. Effective altruists believe that it's not enough to simply do good; we mu