In Cambodia, 79% of married women of reproductive age wish to limit or delay births, yet only 27% are using a modern method of contraception. The purpose of this mixed-method dissertation is to examine the determinants and barriers to contraceptive use in this population. The two specific aims are to 1) use quantitative data examine the associations between social support and contraceptive use among Cambodian women of low vs. high parity; and 2) use qualitative data to understand the different characteristics and barriers to method use of women who use contraceptives, women who have discontinued contraceptive use and women who have never used a modern method. The quantitative study (aim 1) surveyed a representative sample of married women ages 15-49 from two rural provinces in Cambodia (Kampong Thom and Kampot) and measured current contraceptive use, demographic characteristics and items related to contraceptive social support of husbands, peers and elders. Multivariate logistic regression methods were used to measure the association between contraceptive use and social support and models were stratified by low (=3 live births), The qualitative study (aim 2) used in-depth interviews and focus group discussions with different contraceptive user types to understand unique barriers and motivations of users, discontinuers and non-users of contraceptive methods. The quantitative paper shows significant associations between husband's support and contraceptive use. For all women, a husband's positive attitude towards methods and ease of communication with the husband are associated with higher contraceptive use; however, when the husband has full decision-making power, the likelihood of method use decreases among high-parity women. For low-parity woman, perceiving that peers use modern methods increases the likelihood of contraception. In both groups elders' negative opinions about contraceptive use decrease actual use. The qualitative findings show that rumors of myths and misconceptions about side effects are main barriers to the use and were wide-spread among all women. Differences between the three user types show that positive husband support, access to health providers and a high degree of self-efficacy for contraceptive use contribute to successful initiation and continuation of modern methods.