Perceived safer than tobacco cigarettes, prevalence of electronic cigarette (e-cigarette) use is increasing. Analyses of cartridges suggest that e-cigarettes may pose health risks. In light of increased use and the potential for consequences, we searched Google Scholar and Pubmed in July of 2013 using keywords, such as e-cigarette and vaping, to compare differences and similarities in prevalence and correlates of e-cigarette use among adolescents (grades 6-12) versus adults (aged ≥18 years). Twenty-one studies focused on e-cigarette use. Ever-use increased among various age groups. In 2011, ever-use was highest among young adults (college students and those aged 20-28; 4.9%-7.0%), followed by adults (aged ≥18; 0.6%-6.2%), and adolescents (grades 6-12 and aged 11-19; <1%-3.3%). However, in 2012 adolescent ever-use increased to 6.8% and, among high school students, went as high as 10.0%. While the identified common correlate of e-cigarette use was a history of cigarette smoking, a notable proportion of adolescents and young adults who never smoked cigarettes had ever-used e-cigarettes. E-cigarette use was not consistently associated with attempting to quit tobacco among young adults. Adults most often reported e-cigarettes as a substitute for tobacco, although not always to quit. Reviewed studies showed a somewhat different pattern of e-cigarette use among young people (new e-cigarette users who had never used tobacco) versus adults (former or current tobacco users). Research is needed to better characterize prevalences, use correlates, and motives of use in different population groups, including how adolescent and young adult experimentation with e-cigarettes relates to other types of substance use behaviors.