©Greta Hsu, Jessica Y Sun, Shu-Hong Zhu. Background: The electronic cigarette (e-cigarette) industry has grown in size and organizational complexity in recent years, most notably with the entry of major tobacco companies in 2012 and the proliferation of vape shops. Many brands maintain retail websites that present e-cigarette marketing claims and sell directly to consumers. Understanding of the evolving composition of different types of e-cigarette brand websites is currently underdeveloped. Objective: This paper presents how e-cigarette brand websites surveyed in 2013-2014 evolved by 2016-2017, and how the websites run by different types of e-cigarette producers currently differ. Methods: In 2016-2017, we revisited 466 e-cigarette brand websites surveyed in 2013-2014, 288 of which were extant, and identified 145 new English-language websites. We compared product designs, marketing claims, and age-based warnings presented by types of e-cigarette producers: major tobacco companies, independent vape shops, and independent internet-only companies. Results: Among the 433 websites examined in 2016-2017, 12 were owned by major tobacco companies, 162 operated a physical vape shop, and 259 were internet-only operations. Closed-system product designs were sold by 83% (10/12) of tobacco-owned brands. In comparison, 29.0% (47/162, P<.001) of vape shop and 55.2% (143/259, P=.06) of internet-only brands sold closed-system designs. Compared with vape shop and internet-only brands, tobacco-owned brands offered a smaller set of product models (P values <.001) and a narrower range of flavors (P values <.01), with greater emphasis on the traditional combustible cigarette flavors of tobacco and menthol (P values <.001). Tobacco-owned brands also offered a narrower range of nicotine options than the vape shops (P=.002) and were less likely to offer nicotine-free e-liquid compared with internet-only and vape shop brands (P values <.001). Finally, 83% (10/12) of tobacco-owned brand websites featured age verification pop-up windows. In comparison, only 50.2% (130/259) of internet-only brands (P=.01) and 60.5% (98/162) of vape shop brands (P=.06) featured age verification windows. Websites surveyed in both 2013-2014 and 2016-2017 became more likely to sell open-system mods (P<.001) and sold an increased number of product models (P<.001), flavors (P<.001), and nicotine options (P<.001). Prevalence of several types of claims decreased significantly, including indirect claims regarding smoking cessation (P<.001), claims regarding e-cigarettes as healthier (P<.001), less expensive (P<.001), and usable in more places (P<.001) compared with combustible cigarettes. Conclusions: The number of e-cigarette brands has not appeared to increase since 2014, even as website messaging evolved, with brands owned by tobacco companies and vape shops pulling in opposite directions. Brands owned by tobacco companies offered a limited range of e-cigarette products, whereas brands owned by vape shops emphasized a panoply of flavor and nicotine options. Furthermore, the Food and Drug Administration’s regulatory action may influence the types of e-cigarette products offered and the market shares of various companies.