Nonmetallic inclusions are well known to influence product quality and process stability in the production of steel. A process step that is very sensitive to the presence of nonmetallic inclusion (NMI) is continuous casting. Here, the so-called clogging phenomenon can occur, resulting in a distinct disruption of the casting process and decreased steel quality. The presence of nonmetallic inclusions considerably contributes to the build-up of deposits in the submerged entry nozzle provoking instabilities in the flow control system. Numerous research studies have been subject to different clogging mechanisms and related influencing parameters. Interfacial properties significantly influence the behavior of inclusions in the steel–refractory system. The present review demonstrates state of the art concerning the role of NMIs in the appearance of clogging. Particular focus is put on the wetting behavior between the different phases and their consequence for the deposition process. Industrial observations and laboratory methods are summarized and discussed; potential countermeasures are evaluated. A steel group that is especially prone to clogging are Ti- ultra low carbon (ULC) steels. An overview of the current understanding of their high clogging tendency and possible influences is presented, considering thermodynamic and interfacial aspects.