Breast cancer is one of the most debilitating human carcinomas with second highest mortality rate after lung cancer in women. Recent advancement in genetic and biochemical analyses has deciphered the molecular pathways involved in breast cancer development. Wnt signal has long been established to play a critical role in normal development as well as in tumorigenesis. In this review, we summarize the role of Wnt signal in the development of mammary carcinoma, the molecular mechanism via which Wnt signal exerts its malignant potential and various nodal points in the Wnt cascade that can be targeted for drug development and cancer treatment.