Almost all organisms, from bacteria to humans, possess catalytic systems that promote disulfide bond formation‐coupled protein folding, i.e. oxidative protein folding. These systems are necessary for the biosynthesis of many secretory and membrane proteins, such as antibodies, major histocompatibility complex molecules, growth factors, and insulin. Over the last decade, structural studies have made striking progress in this field of research, identifying how oxidative systems operate in a specific and regulated manner to maintain redox and protein homeostasis within cells. Interestingly, more and more novel catalysts that promote disulfide bond formation have been discovered in mammals, suggesting that the oxidative protein folding network is even more complicated in higher eukaryotes than previously thought. This review highlights the physiological roles and molecular bases of the disulfide bond formation pathways that have evolved in the bacterial periplasm and the endoplasmic reticulum of fungi and mammals. Accumulating knowledge about disulfide bond formation networks widely distributed throughout the biological kingdom has significantly advanced our understanding of the cellular mechanisms dedicated to protein quality control. To catalyze oxidative folding of secretory and membrane proteins, several disulfide bond‐formation pathways exist in the endoplasmic reticulum. Ero1α and Prx4 are representative mammalian enzymes that oxidize PDI family member proteins. We review physiological roles and molecular bases of the disulfide bond formation network present in the biological kingdoms including bacteria, fungi and mammals.