This study investigated middle school students' conceptions of engineering. Participants were sixth through eighth grade members of afterschool engineering clubs. Thus, the study contributes to understanding middle school students' knowledge of engineering, and also to how afterschool activities shape students' conceptions of engineering. Researchers have increasingly attended to students' perceptions of themselves as engineers, and their attitudes towards engineering majors and careers. However, little research has investigated middle school students' conceptions of engineering-what engineering is and what engineers do. The purpose of this study was to understand how middle school students who join afterschool engineering clubs conceptualize engineering and how engineering afterschool club experiences influence students' conceptions of engineering. The results of our study indicate that many participants had limited conceptions of engineering and suggest a need to connect design activities with knowledge of engineering.