E-cigarettes (ECs) have gained significant attention in recent years. They have been introduced in jurisdictions with divergent existing laws that affect their legality. This provides the opportunity for natural experiments to assess effects of such laws in some cases independent of any formulated government policy. We compare patterns of EC awareness and use over a 3 year period in Australia where laws severely restrict EC availability, with awareness and use in the United Kingdom where ECs are readily available. Data analyzed come from Waves 8 and 9 (collected in 2010 and 2013, respectively) of the International Tobacco Control surveys in Australia and the United Kingdom (approximately 1,500 respondents per wave per country). Across both waves, EC awareness, trial, and use among current and former smokers were significantly greater in the United Kingdom than in Australia, but all 3 of these measures increased significantly between 2010 and 2013 in both countries, and the rate of increase was equivalent between countries. Seventy-three percent of U.K. respondents reported that their current brands contained nicotine as did 43% in Australia even though sale, possession and/or use of nicotine-containing ECs without a permit are illegal in Australia. EC use was greater among smokers in both countries, at least in part due to less uptake by ex-smokers. EC awareness and use have risen rapidly between 2010 and 2013 among current and former smokers in both Australia and the United Kingdom despite different EC regulatory environments. Substantial numbers in both countries are using ECs that contain nicotine.