An important new survey on Americans’ religious behaviors and attitudes was released this morning. The American Religious Identification Survey was first fielded in 1990 and was updated in 2001 and now in 2008.

The survey shows that just about across the board, Americans are less religious today than they were two decades ago. From USA Today:

The percentage of people who call themselves in some way Christian has dropped more than 11% in a generation. The faithful have scattered out of their traditional bases: The Bible Belt is less Baptist. The Rust Belt is less Catholic. And everywhere, more people are exploring spiritual frontiers — or falling off the faith map completely.

These dramatic shifts in just 18 years are detailed in the new American Religious Identification Survey (ARIS), to be released today. It finds that, despite growth and immigration that has added nearly 50 million adults to the U.S. population, almost all religious denominations have lost ground since the first ARIS survey in 1990.

Of special interest is the “none” category — people who answer they have no religion or spirituality. That share is 15%. From the article:

So many Americans claim no religion at all (15%, up from 8% in 1990), that this category now outranks every other major U.S. religious group except Catholics and Baptists. In a nation that has long been mostly Christian, “the challenge to Christianity … does not come from other religions but from a rejection of all forms of organized religion,” the report concludes.

Here is a presentation by Barry Kosmin, study director, about the “Nones.”