In the 1950s and 1960s the apparent similarities between the adaptable abstract computing machine and the human mind led many to expect the rapid emergence of human-quality intelligence from computers. They were disappointed. Human brains and human thinking seem to be much more complicated than we thought, and the particular strengths of machine intelligence are perhaps of a di erent sort. While asking how designers think has not been immediately productive, asking what designers do has been. Focusing on observable information-processing behaviors-the creation, sharing, and modi cation of calculations, drawings, and other documents-has produced the current state-of-the-art in design practice.