Killing a cell through apoptosis ultimately rests on the mechanical destruction of the structure and function of cellular machineries. Understanding the mechanics of one particular function is usually the last step in our quest to decipher the underlying molecular mechanism. Execution of apoptosis is initiated by the activation of initiator caspases, which is mediated by specific adaptor protein complexes generally known as apoptosomes. This review discusses the assembly, structure and function of the heptameric Apaf-1 apoptosome, the tetrameric CED-4 complex, the octameric Dark apoptosome, and the death-inducing signaling complex (DISC).