In this paper, the author presents a study which explored K-8 preservice teachers' concept images and mathematical definitions of polygons. This study was carried out in which K-8 teacher candidates enrolled in an elementary mathematics content course were asked to sort, identify, and provide definitions of such shapes including triangles, quadrilaterals, and other n-gons. Of interest to the author was the collection of concept images these teacher candidates possessed of certain polygons. The results reported in this paper focus on the teacher candidates' completion of those tasks involving triangles and hexagons. The author suggests that mathematics educators need to provide teacher candidates with experiences that will enable them to develop that strong, connected foundational knowledge needed to teach K-8 mathematics. (Contains 6 figures.)