Since the early recognition that the murine Wnt locus is frequently activated by insertion of the mouse mammary tumour virus, the Wnt pathway has become increasingly associated with both normal and abnormal mammary gland development. This link is further underlined by an emerging role for Wnt deregulation in human mammary neoplasia. The control of transcription through the Wnt signaling pathway is clearly a prime element of this role; however, components of the Wnt pathway possess many functions in addition to their signaling activity, interacting with multiple factors implicated in cellular control processes. Prominent amongst these are the cadherins, which have characterized roles in mediating cell-cell adhesion, and which have been independently implicated in mammary neoplasia. The close interplay between these 2 systems will be discussed in this review with reference both to the normal development of the mammary gland and to the onset of neoplasia in this tissue.