Non-metallic 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 non-metallic inclusions is continuous casting. Here, the so-called clogging phenomenon can occur, resulting in a distinct disruption of the casting process and a decreased steel quality. The presence of non-metallic 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 of different clogging mechanisms and related influencing parameters. Interfacial properties significantly influence the behavior of inclusions in the steel-refractory system. The present review demonstrates the state of the art concerning the role of non-metallic inclusions for 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-ULC steels. An overview of the current understanding of their high clogging tendency and possible influences is presented, considering thermodynamic and interfacial aspects. This article is protected by copyright. All rights reserved.