The BCL-2 family of proteins, including both pro- and anti-apoptotic members, regulates mitochondrial outer membrane permeabilization (MOMP), a critical step in apoptosis. The BCL-2 family is divided into three groups based on the presence of BCL-2 homology (BH) domains. Anti-apoptotic proteins, such as BCL-2, BCL-xL, and MCL-1, inhibit pro-apoptotic proteins like BAX and BAK, which are essential for MOMP. BH3-only proteins, such as BID, BIM, and PUMA, can either directly activate BAX and BAK or neutralize anti-apoptotic proteins, leading to MOMP. Two main models explain this process: the "anti-apoptotic protein neutralization" model, where BH3-only proteins neutralize anti-apoptotic proteins to release BAX and BAK, and the "direct activation" model, where BH3-only proteins directly activate BAX and BAK. Recent studies suggest that both models may be involved, with BH3-only proteins performing both functions to efficiently engage MOMP and apoptosis. The debate continues over the exact mechanisms and interactions within the BCL-2 family that lead to MOMP, with implications for cancer therapy and drug development. Understanding these interactions is crucial for developing effective treatments targeting apoptosis pathways.The BCL-2 family of proteins, including both pro- and anti-apoptotic members, regulates mitochondrial outer membrane permeabilization (MOMP), a critical step in apoptosis. The BCL-2 family is divided into three groups based on the presence of BCL-2 homology (BH) domains. Anti-apoptotic proteins, such as BCL-2, BCL-xL, and MCL-1, inhibit pro-apoptotic proteins like BAX and BAK, which are essential for MOMP. BH3-only proteins, such as BID, BIM, and PUMA, can either directly activate BAX and BAK or neutralize anti-apoptotic proteins, leading to MOMP. Two main models explain this process: the "anti-apoptotic protein neutralization" model, where BH3-only proteins neutralize anti-apoptotic proteins to release BAX and BAK, and the "direct activation" model, where BH3-only proteins directly activate BAX and BAK. Recent studies suggest that both models may be involved, with BH3-only proteins performing both functions to efficiently engage MOMP and apoptosis. The debate continues over the exact mechanisms and interactions within the BCL-2 family that lead to MOMP, with implications for cancer therapy and drug development. Understanding these interactions is crucial for developing effective treatments targeting apoptosis pathways.