Editors' Summary: CERCLA §107 contains a third-party affirmative defense provision for owners of hazardous waste sites who exercised due care. Despite the abundance of CERCLA litigation, until recently no clear understanding of due care had yet emerged. But now, a series of New York federal court opinions suggest that due care turns on the owner's actions at the time the owner becomes aware of the contamination. This Article surveys the due care case law and focuses on the recent New York decisions. The Article concludes that to benefit from the protection of the due care affirmative defense, a site owner should notify appropriate governmental authorities as soon as the owner learns of possible contamination and cooperate with authorities to determine the scope of the contamination, endeavor to limit the spread of contamination, and remain personally involved in the investigation and remediation.