This article examines women's covert use of contraceptives, that is, their use of a method without their husbands' knowledge. Three questions are addressed: (1) How is covert use measured? (2) How prevalent is it? and (3) What are the factors underlying covert use? Existing studies are used together with survey and qualitative data collected in 1997 in an urban setting in Zambia from married women and their husbands. Women's covert use of contraceptives is estimated to account for 6 to 20 percent of all current contraceptive use, and it is more widespread when contraceptive prevalence is low. The multivariate analysis indicates that difficult spousal communication about contraception is the strongest determinant of covert use. Husbands' disapproval of contraception works through spousal communication rather than as a direct influence on covert use. Husbands' pronatalism had no significant effect. The article concludes with implications of covert use for reproductive health and family planning programs, especially women's (and men's) needs for confidential services.