Guidelines endorse the use of chemoprevention for breast cancer risk reduction. This study examined the barriers and facilitators to chemoprevention use for Australian women at increased risk of breast cancer, and their clinicians. Surveys, based on the Theoretical Domains Framework, were mailed to 1,113 women at ≥16% lifetime risk of breast cancer who were enrolled in the Kathleen Cuningham Foundation Consortium for Research into Familial Breast Cancer cohort study (kCon-Fab), and their 524 treating clinicians. Seven hundred twentyfivewomen (65%) and 221 (42%) clinicians responded. Only 10 (1.4%) kConFab women had ever taken chemoprevention. Three hundred seventy-eight (52%) kConFab women, two (3%) breast surgeons, and 51 (35%) family physicians were not awareof chemoprevention. Forwomen, thestrongestbarriers to chemopreventionwere side effects (31%) and inadequate information (23%), which operate in the Theoretical Domains Framework domains of "beliefs about consequences"and "knowledge,"respectively. Strongest facilitators related to tamoxifen's long-term efficacy (35%, "knowledge,""beliefs about consequences,"and "goals"domains), staying healthy for family (13%, "social role"and "goals"domains), and abnormal breast biopsy (13%, "environmental context"domain). The strongest barrier for family physicians was insufficient knowledge (45%, "knowledge"domain) and for breast surgeons was medication side effects (40%, "beliefs about consequences"domain). The strongest facilitators for both clinician groups related to clear guidelines, strong family history, and better tools to select patients ("environmental context and resources"domain). Clinician knowledge and resources, and beliefs about the side-effect consequences of chemoprevention, are key domains that could be targeted to potentially enhance uptake.