Though giving to religion in the U.S. topped $100 billion in 2010—putting it at nearly 1 percent of GDP—no monthly index charts the nation's leading religious indicators. Even the Census Bureau, the nation's most comprehensive data-gathering enterprise, avoids collecting basic information about religion. No constitutional provision bars the collection of such information, but the government has long hesitated to intrude in the affairs of religious bodies. So most of what we know about religion in America is based on what individuals and groups reveal voluntarily to independent researchers. Fortunately, a small number of public foundations, most notably Lilly Endowment, the John M. Templeton Foundation and the Pew Charitable Trusts, continue to fund basic research on the state of American religion.