Cellular redox is controlled by the thioredoxin (Trx) and glutathione (GSH) systems that scavenge harmful intracellular reactive oxygen species (ROS). Oxidative stress also evokes many intracellular events including apoptosis. There are two major pathways through which apoptosis is induced; one involves death receptors and is exemplified by Fas-mediated caspase-8 activation, and another is the stress- or mitochondria-mediated caspase-9 activation pathway. Both pathways converge on caspase-3 activation, resulting in nuclear degradation and cellular morphological change. Oxidative stress induces cytochrome c release from mitochondria and activation of caspases, p53, and kinases, including apoptosis signal-regulating kinase 1 (ASK1), c-Jun N-terminal kinase, and p38 mitogen-activated protein kinase. Trx inhibits apoptosis signaling not only by scavenging intracellular ROS in cooperation with the GSH system, but also by inhibiting the activity of ASK1 and p38. Mitochondria-specific thioredoxin (Trx-2) and Trx peroxidases (peroxiredoxins) are suggested to regulate cytochrome c release from mitochondria, which is a critical early step in the apoptotis-signaling pathway. dATP/ATP and reducing factors including Trx determine the manifestation of cell death, apoptosis or necrosis, by regulating the activation process and the activity of redox-sensitive caspases. As mitochondria are the most redox-active organelle and indispensable for cells to initiate or inhibit the apoptosis process, the regulation of mitochondrial function is the central focus in the research field of apoptosis and redox.