Abstract Mitochondrial apoptosis is a stress-triggered cell death pathway implicated in health and disease. This pathway is readily blocked in cancer. Mitochondrial poration is at the heart of mitochondrial apoptosis being regulated by the BCL-2 proteins. This process regulates the release from mitochondria of prodeath factors that activate the caspase cascade which dismantles apoptotic cells. Mitochondrial poration is executed by the BCL-2 protein BAK. Here we propose to delineate the mechanism of mitochondrial poration by BAK, which is elusively defined and controversial. In particular, we propose to elucidate 1) the mechanism of BAK activation, 2) BAK association with and poration of membranes, and 3) BAK recognition and sequestration by prosurvival BCL-2 proteins. To accomplish these aims we will use a multi-pronged approach including high-resolution structural biology, biophysics, biochemistry, and cell biology to generate a complete picture of mitochondrial poration by BAK. Upon successful completion we will redefine our mechanistic understanding of this process, and we will reveal innovative ways to target apoptosis in pathophysiology.