When physicians practice defensive medicine by ordering extra tests and procedures that have little or no benefit solely to avoid malpractice lawsuits, they can reduce the quality of the care they provide and increase health care costs. But the introduction of reliable clinical practice guidelineswhich are recommendations for optimizing patient care based on scientific evidencepromises to help reduce overutilization of unnecessary procedures and set standards of good care. This paper explores whether such guidelines might also serve as liability safe harbors for caregivers, shielding them from malpractice claims for failing to provide services not included in a guideline. Authors examine how legislating safe harbors would work in theory and practice, and suggests that while guidelines hold promise for cutting wasteful defensiveness, practical feasibility limits their reach.