AIMS: Studying users of e-cigarettes is important to help determine whether these devices aid smoking cessation. Obtaining data in representative samples is difficult, but online surveys of users may begin to build a picture. Therefore, this study aimed, through a large online survey, to describe usage and characteristics of users of e-cigarettes. DESIGN: Cross-sectional internet survey between 2012 and 2014. SETTING AND PARTICIPANTS: A total of 2807 current e-cigarette users enrolled via e-cigarette and smoking cessation websites, who lived in France (n = 988), the United States (n = 579), Switzerland (n = 310), the United Kingdom (n = 143) and other countries (n = 787). MEASUREMENTS: Type of e-cigarette used: pre-filled cartridges (n = 71), unmodified refillable tanks (n = 758), modified refillable tanks (n = 392), patterns of use, perceived effects. FINDINGS: Pre-filled models were perceived to be less effective than unmodified refillable tanks for smoking cessation by former smokers ('definitely helped': 74% vs. 94%, P < 0.001) and by current smokers for smoking reduction ('definitely helped': 37% vs. 78%, P < 0.001). Users modified their e-cigarettes mainly to obtain a better taste ('very true' 60%, 55.5-64.5%). Modified tanks were perceived to make it easier to abstain from smoking than unmodified tanks 95% vs. 89%, P < 0.001); 34% of users of pre-filled cartridges, 60% of users of unmodified tanks and 83% of users of modified tanks were men (P < 0.001). CONCLUSIONS: Newer-generation e-cigarettes were perceived to be more satisfactory and more effective for refraining from smoking than older models. Women tended to use pre-filled, unmodified models, which were perceived by participants to be the least effective in terms of abstaining from smoking.