The dynamics of star-forming regions - which mechanisms set the cluster formation efficiency?

The fraction of star formation that results in bound stellar clusters (cluster formation efficiency or CFE) is a central quantity in many studies of star formation, star clusters and galaxies. Recent results suggest that contrary to popular assumption, the CFE is not (solely) set by gas expulsion, but is also influenced by the primordial environment, although its precise behaviour remains unknown. Here it is discussed which mechanisms set the CFE, which recent advancements have been made to disentangle their contributions, and which studies are needed in the near future to achieve a quantitative understanding of the CFE.