Professional Development Standard C of the National Science Education Standards recommends that professional development activities for teachers "provide opportunities to learn and use the skills of research to generate new knowledge about science" (NRC 1996, 68). This chapter considers four issues underlying this standard: (1) What does it mean for a teacher to be a researcher? (2) How do teachers inquire into science learning and teaching? (3) Why would they undertake such inquires? (4) In what ways do they use and communicate their findings?