Editors' Summary: Environmental auditing has become one of the most widely used techniques for detecting and preventing environmental problems before they get out of hand. Increasingly, corporations with sophisticated environmental staffs are using the technique to evaluate not only the corporation's own pollution concerns but also those of corporations that are possible partners in a merger or acquisition. Environmental auditing is thus becoming part of the "due diligence" practiced in evaluating major business transactions. In this Article, the author describes the needs for environmental due diligence auditing and the contractual issues underlying it. He explains how corporations should plan and carry out environmental due diligence auditing, and then analyzes typical problems that arise and evaluates responses to them.