Additional information: The supplement Tables can be found in the Online Data Supplement at http://chestjournal.chestpubs.org/ content/141/2_suppl/e531S/suppl/DC1. Stroke is a serious complication of AF, but its risk varies considerably across different groups of patients with AF. Antithrombotic prophylaxis for stroke is associated with an increased risk of bleeding. We provide recommendations for antithrombotic treat- ment based on net clinical bene t for patients with AF at varying levels of stroke risk. Oral anticoag- ulation is the optimal choice of antithrombotic therapy for patients with AF at high risk of stroke (eg, CHADS2 score 2). At lower levels of stroke risk, antithrombotic treatment decisions will require a more individualized approach that takes into con- sideration patient values and preferences, bleeding risk, and the presence of non-CHADS2 stroke risk factors. The role of oral anticoagulation for the pre- vention of stroke in patients with AF will evolve as the results of large, ongoing, phase 3 RCTs of new oral anticoagulants are published and as experience with these new agents in clinical practice continues to grow. Acknowledgments Author contributions: As Topic Editor, Dr You oversaw the development of this article, including the data analysis and sub- sequent development of the recommendations contained herein. Dr You: contributed as Topic Editor. Dr Singer: contributed as a panelist. Dr Howard: contributed as a panelist. Dr Lane: contributed as a panelist. Dr Eckman: contributed as a resource consultant. Dr Fang: contributed as a panelist. Dr Hylek: contributed as a panelist. Dr Schulman: contributed as a panelist. Dr Go: contributed as a panelist. Dr Hughes: contributed as a panelist. Dr Spencer: contributed as a panelist. Dr Manning: contributed as a panelist. Dr Halperin: contributed as a panelist. Dr Lip: contributed as Deputy Editor and senior author. Financial/non nancial disclosures: The authors of this guide- line provided detailed con ict of interest information related to each individual recommendation made in this article. A grid of these disclosures is available online at http://chestjournal. chestpubs.org/content/141/2_suppl/e531S/suppl/DC1. In summary, the authors have reported to CHEST the following con icts of interest: Over the past 3 years, Dr Singer has received grant support from the Eliot B. and Edith C. Shoolman fund of Massachusetts General Hospital (MGH) to study stroke in atrial brillation. He has also received research grant support (through MGH) from Daiichi-Sankyo, Inc, to study hemorrhage risk in patients with atrial brillation taking warfarin. Dr Singer has been supported by the National Institutes of Health (National Heart, Lung, and Blood Institute and National Institute on Aging) grant funding to study stroke risk in patients with atrial brillation. 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