To engage meaningfully with scientific models, undergraduate students must come to understand what counts as a scientific model and why. To gain a sense of the characteristics that undergraduate chemistry students ascribe to scientific models, we analyzed survey data that address students' ideas about both model criteria in general and criteria related to specific models of chemical phenomena. The findings suggest that undergraduate general chemistry students possess some productive and some intuitive ideas about the characteristics of scientific models but may not have systematic or coherent conceptions about models across contexts.