Examination of anonymous records of donations by 1.8 million people shows that many organizations that rely on public donations to achieve their missions experience very high turnover rates in their donor rolls. This pattern leads to high costs of fundraising for some organizations. Other groups, though, see much higher rates of retention year after year, suggesting that it is possible for more organizations to trim costly acquisition campaigns and the loss of potential long-term supporters. Donor Retention Matters reports on some key findings from the Fundraising Effectiveness Project. Continuing research will explore in more detail the underlying trends and patterns that affect this measure of nonprofits' connections with the communities they serve.