Breast cancer is the most common type of cancer in women worldwide. About ten percent of women are confronted with breast cancer in their lives. Breast Cancer can be most efficiently treated if detected at an early sage. Imaging of the breast can be accomplished using several modalities such as: X-ray, MRI, CT, Ultrasound, and now Molecular Imaging. Image registration plays a critical role in breast imaging. It provides aid to better visualization of lesions on bilateral or temporal X-ray mammograms, or in the fusion of different modalities acquired using different principles of physics. The non-rigid, inhomogeneous, anisotropic and temporally changing nature of breast tissue make breast image registration a challenging task. This paper presents an overview of the current state-of-the-art in the breast image registration techniques. Methods are classified according to the modalities involved in the registration process. Intra-modality registration techniques focus on X-ray mammogram registration, while inter-modality techniques will cover the registration of X-ray with other modality. Validation of breast registration methods is also discussed.