Purpose: Despite evidence that adolescents become addicted to nicotine even after limited use, adolescents believe they can experiment with or smoke cigarettes for a few years and easily quit. The goal of this study was to examine adolescents' understanding of the definition and process of nicotine addiction using a mixed-methods approach. Method: A total of 367 adolescents with and without smoking experience rated the perceived risk for addiction, still being a smoker in 5 years, and ability to quit smoking. A subsample of adolescents (N = 41) were interviewed about their conceptualization and understanding of nicotine addiction. Within-participants analyses of variance were conducted to assess differences in perceptions of addiction across the three scenarios; thematic analyses of interviews were conducted to assess adolescents' understanding of addiction. Results: Adolescents rated their perceived risk for addiction, still being a smoker in 5 years, and ability to quit as significantly different from one another for three different scenarios (F = 7.81, 47.78, and 70.27, respectively; p < 0.001). Seven themes describing how youth conceptualize and understand addiction emerged from the interview data, including skepticism and uncertainty about addiction, how smoking makes a person feel, and family and friends' experiences. Conclusion: While adolescents have received the message that cigarettes are addictive, they are uncertain regarding the definition of addiction and have not recognized that addiction means experiencing difficulty quitting and continuing to smoke longer than expected. Findings suggest the need for comprehensive messaging regarding nicotine addiction in educational, clinical, and intervention settings and for product warning messages aimed at reducing and preventing tobacco use.