ABSTRACT: Since electronic cigarettes (e-cigarettes) entered the U.S. marketplace in 2007, the landscape has evolved to include different product types (e.g., prefilled cartridge-based and disposable products) and flavored e-liquids (e.g., fruit, candy, mint, menthol, and tobacco flavors), which have contributed to increases in youth use (1,2). E-cigarettes have been the most commonly used tobacco product among U.S. youths since 2014; in 2019, 27.5% of high school students reported current e-cigarette use (3). To assess trends in unit sales of e-cigarettes in the United States by product and flavor type, CDC, CDC Foundation, and Truth Initiative analyzed retail scanner data during September 14, 2014-May 17, 2020, from Information Resources, Inc. (IRI). During this period, total e-cigarette sales increased by 122.2%, from 7.7 million to 17.1 million units per 4-week interval. By product type, the proportion of total sales that was prefilled cartridge products increased during September 2014-August 2019 (47.5% to 89.4%). During August 2019-May 2020, the proportion of total sales that was disposable products increased from 10.3% to 19.8%, while the proportion that was prefilled cartridge products decreased (89.4% to 80.2%). Among prefilled cartridge sales, the proportion of mint sales increased during September 2014-August 2019 (<0.1% to 47.6%); during August 2019-May 2020, mint sales decreased (47.6% to 0.3%), as menthol sales increased (10.7% to 61.8%). Among disposable e-cigarette sales during September 2014-May 2020, the proportion of mint sales increased (<0.1% to 10.5%), although tobacco-flavored (52.2% to 17.2%) and menthol-flavored (30.3% to 10.2%) sales decreased; during the same period, sales of all other flavors combined increased (17.2% to 62.1%). E-cigarette sales increased during 2014-2020, but fluctuations occurred overall and by product and flavor type, which could be attributed to consumer preferences and accessibility. Continued monitoring of e-cigarette sales and use is critical to inform strategies at the national, state, and community levels to minimize the risks of e-cigarettes on individual- and population-level health. As part of a comprehensive approach to prevent and reduce youth e-cigarettes use, such strategies could include those that address youth-appealing product innovations and flavors.