The mammary gland represents an unique model system to allow investigation of factors that underpin biological initiation of apoptotic processes and related signal transduction pathways. One advantage is that the mammary gland, unlike most other organs, has the capacity to go through many cycles of growth, differentiation and anatomical structural development. Indeed, the mammary gland has evolved highly efficient processes (that straddle both lactation and post-lactational phases)  which regulate the balance between cell death and proliferation. This paper will discuss the molecular and cellular aspects of apoptosis in the mammary gland with a particular emphasis on the role of apoptosis in breast cancer development.