This report documents the results of four series of policy exercises conducted under "The Day After... "project. This summary first describes the assumptions, objectives, and approach of the study, including the exercise technique. It then covers each of the four series of exercises. It highlights the participants' discussion and debate and, based on the results of each exercise series, identifies alternative approaches to proliferation-related policy problems. "The Day After... " study revealed that the policy support community in Washington (represented by the participants) has yet to articulate the implications of nuclear proliferation for U.S. defense strategy. Although this report does not advocate any specific policies, its authors urge the U.S. government and the analytic community to study more rigorously the options for addressing nuclear proliferation.