  Recent progress in understanding the emergence of confinement and other
nonperturbative effects in the strong interaction vacuum is reviewed. Special
emphasis is placed on the role of different types of collective infrared
gluonic degrees of freedom in this respect. After a survey of complementary
approaches, models of the QCD vacuum based on center vortices, Abelian magnetic
monopoles and topological charge lumps such as instantons, merons and calorons
are examined. Both the physical mechanisms governing these models as well as
recent lattice studies of the respective degrees of freedom are reviewed.
