Over the years, the content knowledge that a teacher holds has been viewed as essential to his or her teaching. As a result, researchers are exploring the content knowledge that teachers hold and those in teacher education are crafting programs to improve the content knowledge of teachers. With this ongoing interest in this area, it is important to characterize the content knowledge that a science teacher needs. This paper provides a general introduction to science teacher subject matter knowledge and reports on two explorations in this area. One approach involves using scenarios, while the other approach entails concept sketches. These two preliminary approaches have implications for science teacher educators, who are interested in having teachers build their subject matter knowledge during their first years of teaching. They also have implications for studying science teacher knowledge. These studies suggest that there is a need to conceptualize science subject matter knowledge in a way that is educative and formative.