Combustible tobacco use remains the number-one preventable cause of disease, disability, and death in the United States. Electronic nicotine delivery systems (ENDS), which include electronic cigarettes, are devices capable of delivering nicotine in an aerosolized form. ENDS use by both adults and youth has increased rapidly, and some have advocated these products could serve as harm-reduction devices and smoking cessation aids. ENDS may be beneficial if they reduce smoking rates or prevent or reduce the known adverse health effects of smoking. However, ENDS may also be harmful, particularly to youth, if they increase the likelihood that nonsmokers or former smokers will use combustible tobacco products or if they discourage smokers from quitting. The American Association for Cancer Research (AACR) and the American Society of Clinical Oncology (ASCO) recognize the potential ENDS have to alter patterns of tobacco use and affect the health of the public; however, definitive data are lacking. The AACR and ASCO recommend additional research on these devices, including assessing the health impacts of ENDS, understanding patterns of ENDS use, and determining what role ENDS have in cessation. Key policy recommendations include supporting federal, state, and local regulation of ENDS; requiring manufacturers to register with the US Food and Drug Administration and report all product ingredients, requiring childproof caps on ENDS liquids, and including warning labels on products and their advertisements; prohibiting youth-oriented marketing and sales; prohibiting child-friendly ENDS flavors; and prohibiting ENDS use in places where cigarette smoking is prohibited. This policy statement was developed by a joint writing group composed of members from the Tobacco and Cancer Subcommittee of the American Association for Cancer Research (AACR) Science Policy and Government Affairs (SPGA) Committee and American Society of Clinical Oncology (ASCO) Tobacco Cessation and Control Subcommittee of the Cancer Prevention Committee (CaPC). The statement was reviewed by both parent committees (ie, the AACR SPGA Committee and the ASCO CaPC) and was approved by the AACR Boards of Directors on August 6, 2014, and the ASCO Executive Committee on September 18, 2014. This policy statement was published jointly by invitation and consent in both Clinical Cancer Research and Journal of Clinical Oncology. Copyright 2015 American Association for Cancer Research and American Society of Clinical Oncology. All rights reserved. No part of this document may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or storage in any information storage and retrieval system, without written permission by the American Association for Cancer Research and the American Society of Clinical Oncology.