Influencing the policy agenda has long been viewed as one of the most important sources of political power. For decades, scholars have maintained that the president has the most significant role in setting the policymaking agenda in Washington, but little systematic empirical work has been done to measure the president's influence. We explore the president's success in focusing the issue attention of Congress and the mass media by evaluating time-series measures of presidential, mass media, and congressional attention to five issues: crime, education, health care, U.S.Soviet relations, and the Arab-Israeli conflict. We find that most of the time the president reacts, responding primarily to fluctuations in media attention and world events. In domestic policy, we find a more interactive relationship, one that appears to offer the president the opportunity to act in an entrepreneurial fashion to focus the attention of others in the system on major presidential initiatives.