Despite impressive extensions in the scope of women's social and political rights, there have been few extensions of sex-linked boundaries in the prestigious, male-dominated professions. This paper identifies the processes and structure of the professions in the United States which act to limit women's participation and achievement within them. Because their sex status is defined within the culture of professions as inappropriate, women find that the institutionalized channels of recruitment and advancement, such as the protégé system, are not available to them. Various modes of behavior on the part of women and their colleagues are described which are consequences of women's minority position and which reinforce it. Social changes affecting the traditional structures and opening careers in the professional hierarchy are discussed.