This document reviews current techniques for segmenting breast cancer images from mammograms. It discusses various preprocessing techniques to improve image quality including median filtering, mean filtering, and wavelet methods. It then summarizes several segmentation algorithms that have been used for mammograms, including region growing, watershed, k-means clustering, fuzzy c-means, and morphological operations. The goal of segmentation is to partition the image into regions corresponding to different breast tissues to assist in detecting abnormalities. Accurate segmentation is challenging but important for computer-aided diagnosis of breast cancer.