In women, breast cancer is the most common cancer worldwide and the foremost cause of cancer death in less developed countries. The balance between the production of free radicals (radical oxygen species and radical nitrogen species) and their neutralizing antioxidants determines the normal homeostasis of the cell. The oxidative stress resultant of imbalance between the free radicals and antioxidants affects many metabolic pathways and results in pathological consequences, including breast cancer. In the present chapter, we provide an overview of how free radicals alter inter/intracellular pathways and induction of epigenetic alterations using breast cancer as our model. We link the connection between free radicals and breast cancer epigenetics by reviewing the mechanisms of free radicals production, effects of free radicals on nuclear epigenetic modifications (DNA and histone modifications), results of epigenetic changes on gene expression that alters reactive oxygen species (ROS) accumulation, and ROS-microRNA relationship. We also highlight the interplay between oxidative stress and epigenetic drugs in breast cancer and the dietary agents with antioxidant properties as epigenetic modulators in breast cancer.