The U.S. nonprofit sector is large and amazingly diverse. It can be complex—nonprofit is not necessarily the same as tax-exempt, not all tax-exempt organizations are charities, and tax-exempt organizations have special rules they must follow in order to retain their status.
The sector is also changing. In June 2011, the IRS began revoking the exemptions of nonprofits required to file an annual return that have failed to do so for three consecutive years. More than 275,000 nonprofits lost their exemptions with publication of the first Automatic Revocation of Exemption List, which the IRS updates monthly. The impact of this historic change remains to be seen.
Here are some resources for demystifying the nonprofit sector. We'll be adding more, so check back when you have a chance.