Developing Mathematical Ideas (DMI) is a staff development/teacher education program designed to help educators think through the major ideas of K-6 mathematics and examine how children develop those ideas. The goal is to engage teachers in a process of inquiry--into mathematics; into learning mathematics; into students' mathematical thinking, in general, and the thinking of one's own students, in particular. In a DMI seminar, teachers discuss print and video cases, explore mathematical questions, investigate the mathematical thinking of their own students, analyze lessons from innovative curricula, and read and discuss essays about related research. Supported during its development by the National Science Foundation, one link is to the publication and another is to the project development site.