The major function of disulfide bonds is not only the stabilization of protein structures. Over the last 30 years, a change in perspective took place driven by groundbreaking experiments, which promoted disulfide bonds to central players in essential thiol-disulfide exchange reactions involved in signal transduction, thiol protection, and redox homeostasis regulation. This new view stimulated redox research and led to the discovery of novel redox pathways, redox enzymes, and new low-molecular-weight thiols. These redox-sensitive molecules operate along diverse pathways via a dynamic thiol-disulfide mechanism in which disulfide bonds are reversibly formed and reduced, thereby switching the molecules between different conformational and functional states. It is now clear that disulfide bonds play a pivotal role in cellular reduction and oxidation processes. However, in spite of the fundamental cell biological and medical importance of the thiol-disulfide exchange switches, we are only beginning to understand their principles of specificity, their mechanism of action, and their role in signal transduction. Our further progress in understanding the thiol-disulfide switches will strongly depend on the chemical tools and on the technological advances that will be made in the development of new methodologies.