The future of physician's assistants and nurse practitioners will be shaped at least in part by whether, and on what terms, they are defensible at law. This paper explores the way in which the principles of tort law might define primary and secondary liability for these new health professionals. Among the issues discussed in substantial detail are whether a separate standard of care is appropriate, whether the new professionals might function as independent contractors, and the importance of striking an adequate social balance between improved access to health care or cost containment on the one hand and malpractice deterrence or redressment on the other.