E-cadherin and its adhesion complex play an essential role in the adhesion of breast cancer cells and tissues. Members of the complex, such as beta-catenin, act as regulators on cell adhesion, and are involved in cell signalling and transcription regulation. The adhesion complex is a known structure in the control of tumour progression and metastasis. Recent years have seen a rapid expansion in the understanding of the biology and clinical relevance of the complex in breast cancer. The current article summarises recent progresses in the molecular/cellular biology of E-cadherin and its complex and the clinical, diagnostic, prognostic, and therapeutic value of this complex in breast cancer.