Programmed cell death or apoptosis is essential for both the development and maintenance of tissue homeostasis in multicellular organisms. The BCL-2 family members are critical regulators of the apoptotic program, whereas the caspase proteases are the major executioners of this program. Members of the BCL-2 family include both anti- and pro-apoptotic proteins. The BH3-only proteins (e.g., BID) are an important subset of the pro-apoptotic proteins that act as sentinels of intercellular damage. In our laboratory, we are focused on elucidating the mechanisms that balance between cell life and death, and BID is one of our primary tools to study these mechanisms.