Despite years of continued growth, women's participation in physics remains among the lowest of any scientific field. The issue is of great concern to many in the scientific community, spawning talks at conferences, data collection efforts, and speculation about the causes of women's low participation in physics. Although women's participation in higher education overall has now passed the 50% mark at the bachelor's level and is approaching 50% at the PhD level, women earned just 22% of physics bachelor's degrees and 18% of physics PhDs in 2003 (a record high). Women's participation in physics is increasing, although slowly, and the rate of increase has not kept pace with other fields. One field that is notable for having a much higher representation of women is astronomy, which is closely related to physics. In spite of the relationship between the two fields, women are more highly represented in astronomy than in physics. For example, women earned 46% of bachelor's degrees in astronomy in 2003 and 26% of PhDs in astronomy in 2003. The following are appended: (1) Number of PhD degrees earned in physics, 1972-2003; (2)Number of PhD degrees earned in astronomy, 1958-2003; and (3) High school students taking AP physics exams. (Contains 12 tables and 16 figures.)