In 1976, in the landmark case of Tarasoff v. The Regents of the University of California, 1 the California Supreme Court imposed a legal duty on psychotherapists, enforceable by a civil suit for damages, to warn a person who may become a victim of a violent act by a patient. Courts and legislatures in other jurisdictions soon began to examine the subject, and within a decade or so the "duty to warn" became law across much of the United States and an integral part of mental health training and practice. A quarter of a century has now passed and the initially brisk pace of law-making has abated, yielding a relatively clear and stable view of the Tarasoff duty today in the various jurisdictions and thus an opportunity to survey and summarize current law. This, the first of two companion articles, offers such a survey. Fully one-fourth of the states (13) have yet to address this controversial 2 subject definitively (nor is there pertinent federal law), and so a brief critical examination of the duty to warn would also seem warranted. That will be the focus of a second article, to appear in a future issue of the Journal. At the outset, for analytical clarity, three issues that sometimes cloud Tarasoff debate and practice should be sketched briefly.