This is the fourth edition of The Law of Tax-Exempt Healthcare Organizations. The first edition was published in 1995 and featured a mere 680 pages. In this edition, we will be approaching twice that content. This seems a good opportunity to pause and reflect on what has transpired in the nonprofit healthcare sector over these past 17 years. In our original edition, tax-exempt healthcare organizations and the IRS were focused on joint ventures with taxable entities; the creation of integrated delivery systems; the proper tax status for managed care organizations; and the appropriateness of providing benefits for the recruitment and retention of physicians. It is telling that the chapters describing these scenarios were among the least in need of revision for this edition. At present, there are newdevelopments occupying the attention of healthcare organizations and the IRS. These include health reform; the governance of healthcare organizations; the compensation of executives; the continued refinement of Form 990; and a host of new acronyms for their shared alphabet soup, including ACOs (accountable care organizations), RHIOs (regional health information organizations), andQNHIIs (qualified nonprofit health insurance issuers). Certainly the most dramatic development in the field of healthcare in 2012 was the U.S. Supreme Court’s decision in National Federation of Independent Business v. Sebelius upholding most of the Affordable Care Act as constitutional. The Affordable Care Act has done much to impact the law of tax-exempt healthcare organizations. It established new requirements for qualification as a charitable hospital that are proactively focused on outreach, service, and billing and collection practices. On a broader level, by providing for insurance coverage for millions of Americans who previously had none and relied on charity, the Affordable Care Act brought into question for some the need to continue to provide tax exemption for nonprofit hospitals that will be providing less charity care. The Act also calls on the Internal Revenue Service to assist in the implementation of many of its provisions, a development sure to further drain the already limited resources of this agency.