Introduction.- Historical sketch of the discovery and recognition of the function of chaperonins.- Molecular structure of chaperonins.- Folding by enclosure in the chaperonin cavity.- Evolutionary origins and family relations.- Chaperoning mechanisms: folding helpers, folding protectors or misfolding blockers?.- Sequence variations in proteins affecting chaperonin dependence.- Genetic organization of type I chaperonin genes.- Regulation of type I...