As a member of the House Ways and Means Committee, Rep. Lloyd Doggett (D-Texas) has for several years been pushing legislation to shut down abusive tax shelters. He describes the tax shelter phenomenon as "a conspiracy between attorneys, accountants, investment bankers and others that develop schemes, really scams, to dodge taxes in ways that go far beyond legitimate tax planning." Doggett also tells FRONTLINE that he believes meaningful reform, including a prohibition against shelters that lack "economic substance," can only be accomplished by congressional action, but that reform is being blocked by the House leadership, including Ways and Means Chairman Bill Thomas and Majority Leader Tom DeLay, because, according to Doggett, "[The] ultimate goal is to eliminate the progressive income tax."

Everson has served as commissioner of the Internal Revenue Service since May 2003. Because the U.S. tax system is based on "voluntary self-assessment," Everson says that abusive shelters are a danger to the system. "Particularly when you have sophisticated players -- large corporations or high net-worth individuals -- who aren't paying their share [of taxes] because they're gaming the system, that undermines the confidence on the part of individuals that they ought to pay their share," he warns. Everson says that the Bush administration favors stronger disclosure and registration requirements to deal with the tax shelter problem, as well as tougher penalties for promoters and investors. He also says that the IRS has over 100 active investigations of shelter promoters currently underway and that although litigation is not the administration's "most desired tool … we won't shy away from litigation if we have to."

Hamersley is a tax lawyer who joined the Washington National Tax office of KPMG in 1998. He tells FRONTLINE that he was bothered immediately by the firm's aggressive promotion of tax shelters and says that the most abusive shelters were kept secret even from company insiders. According to Hamersley, KPMG made a strategic business decision not to register its tax shelters, as required by the IRS, because "the penalties associated with not registering paled in comparison to the revenues that would be generated by those tax shelters that had to be registered." He also says that the fees KPMG received were determined by the amount of tax savings generated by the shelters and that the firm's top managers drove its shelter promotion. Hamersley says in court documents that he blew the whistle on KPMG after he was asked to sign off on tax matters that he considered to be illegal -- a charge disputed by KPMG.

As managing director of the Federal Policy Group of Clark Consulting, Kies lobbies for the leasing industry. He has many years experience on tax issues, serving as Staff Director of the Joint Committee on Taxation (1995-98) and as Minority Counsel of the House Ways and Means Committee (1982-87). In this interview, he defends cross-border leasing deals as legitimate financial transactions with real economics. He argues that they are transactions that "comfortably fit" within 30 years of leasing tax regulations. Kies says some companies will always "push the envelope" to find innovative ways to shelter income. However, he maintains that in the aftermath of post-Enron reforms, including the Sarbanes-Oxley bill, the problem of abusive tax shelters has largely dissipated. "I believe there truly is a fundamental change in the attitude of taxpayers about [their] willingness to enter into these kind of transactions," Kies says.

Langdon was commissioner of the Large and Mid-Size Business (LMSB) Division of the IRS from 1999 to 2003. Prior to the IRS, Mr. Langdon worked at Hewlett Packard for over 21 years, where he was vice president for the Tax, Licensing and Customs department. In this interview with FRONTLINE, Langdon discusses his perspectives, as both a businessman and an IRS regulator, on how the tax shelter phenomenon took off in the 1990's and the efforts by the IRS to combat the problem. He sees the tax shelter phenomenon as a battle of "greed versus ethics."

Spurred by the Enron investigation, Sen. Carl Levin (D-Mich), the ranking Democrat of the Senate Permanent Subcommittee on Investigations, led an investigation into the development and marketing of abusive tax shelters, with particular focus on the activities of KPMG. In this interview, he recounts the investigation and discusses the need for legislation to increase penalty fees for shelter promoters "to make sure that the penalties are just the same on the guys who cooked up the scheme as for the people who try to benefit from it -- the taxpayers themselves." Levin is hopeful about achieving tax shelter reform: "Enron has unleashed a real movement here to do some proper regulation," he says.

McIntyre is the director of the Institute on Taxation and Economic Policy, a research and advocacy organization whose mission, in the words of its Web site, "is to give ordinary people a greater voice in the development of tax laws." He co-authored a 2000 study of corporate income taxes in the 1990s that found the average tax rate among the top 250 companies to be 20 percent in 1998, as opposed to the standard rate of 35 percent. "Lately we think that rate is down to about 15 percent," he says. McInytre tells FRONTLINE that over the past 50 years, corporations paid an average of 17 percent of the total federal tax take, and that now the corporate share of total tax revenues is down to 7 percent. He argues that House Ways and Means Committee Chairman Bill Thomas and the White House have been stumbling blocks to reform. "Both of those have just pushed very hard to maintain shelters the way they are, he says.

A Republican businessman, Rossotti was tapped by President Clinton to become the IRS commissioner in 1997 and served in this position for five years. He is also the author of the forthcoming book, Managing in the Bull's-Eye: Turning Around the IRS, the Organization with the Most Customers and the Lowest Approval Rating in America. In this interview, Rossotti describes his shock at the degree to which the problem of bogus tax shelters had infected the tax system. He tells FRONTLINE that in his estimation, the U.S. government loses between $250 billion and $300 billion each year due to nonpayment of taxes, and that he believes tax shelters are the biggest single piece of the problem. Rossotti says the IRS was hopelessly understaffed and underfunded in trying to keep up with tax fraud. It was, he says, like "taking a knife into a gun fight." He believes that the tax shelter problem will rebound as the economy improves and says that the only way to solve the problem is for Congress to pass an economic substance law that outlaws any transaction whose sole purpose is a tax benefit.

Currently president of Harvard University, Summers served as Secretary of the Treasury in the Clinton administration. During his tenure at Treasury, Summers was troubled by the widening gap between corporate profits and corporate tax payments. Summers says the proliferation of bogus tax shelters threatens the viability of the entire tax system. "When some of the powerful and most well-off elements in society decide to withdraw from paying taxes, that is a moral failure," he tells FRONTLINE.