Understanding how students develop biology interests and the roles interest plays in biology contexts could help instructors and researchers to increase science, technology, engineering, and mathematics students' motivation and persistence. However, it is currently unclear how interest has been defined or measured in the biology education research literature. We analyzed this body of literature to determine how interest has been defined and used by the biology education research community. Specifically, we determined the extent to which previously published work drew on theories that conceptualize interest. Further, we identified studies that measured student interest in biology and characterized the types of measures used. Our findings indicate that biology education researchers typically describe interest as a relationship involving positive feelings between an individual and a physical object, activity, or topic of focus. We also found that interest is often not defined, theories involving interest are not often consulted, and the most common measures of interest only assess a single aspect of the construct. On the basis of these results, we make suggestions for future research seeking to examine biology students' interest. We hope that this analysis can serve as tool for biology educators to improve their own investigations of students' interest and measure outcomes of interest-generating educational activities.