Protein stability, oligomer assembly, localization, and regulation often depend on formation of disulfide cross-links. Sulfhydryl oxidase enzymes catalyze de novo disulfide formation and carry out intra- and intermolecular dithiol/disulfide relays to transfer the disulfides to substrate proteins. Secreted and cell-surface proteins typically acquire disulfides in the endoplasmic reticulum (ER), where multiple enzyme families exist to catalyze cysteine oxidation and disulfide isomerization. Furthermore, a quality control mechanism is thought to patrol the exit from the early secretory pathway, retaining or retrieving incompletely oxidized proteins. It is therefore intriguing that an additional catalyst of disulfide bond formation, an enzyme known as Quiescin sulfhydryl oxidase (QSOX), is found downstream of the ER, i.e., in the Golgi apparatus and secreted from certain cell types. QSOX is conserved in animals and expressed in many tissues, with particularly high levels observed during development and in certain cancers. However, little is known about the biological function of QSOX, its particular molecular targets, or what distinguishes those targets from proteins that are oxidized by conventional routes in the ER. We have shown that QSOX has a role in assembling a functional extracellular matrix (ECM) in fibroblast cell cultures. Recent findings indicate that the enzyme does not cross-link ECM components in a “kiss-and-run” fashion but rather docks onto ECM fibrils and presumably functions while bound within the ECM mesh. Disulfide bond formation, a widespread and readily reversible post-translational modification, appears to be promoted along the secretory pathway, and not just during the first folding of nascent proteins in the ER.