Purpose: Longitudinal studies indicate that e-cigarette use among youth and young adults is associated with cigarette smoking initiation. The purpose of this study was to identify reasons why nonsmoking young adults transition from e-cigarette use to cigarette smoking. Methods: The study used concept mapping (CM), a mixed-method participatory approach. Fiftyfive college students who endorsed initiation of e-cigarettes before cigarettes (lifetime e-cigarette uses ! 100 and ! 100 cigarettes in lifetime) completed at least one part of the study. In an online program, participants brainstormed (n ¼ 54) statements describing reasons for transition from e-cigarette use to cigarette smoking, sorted statements (n ¼ 46) into conceptually similar categories, and rated (n ¼ 47) how true each statement was for them. Results: Participants generated 60 unique statements, and multidimensional scaling analysis generated eight thematic clusters characterizing reasons for transition which included the following: