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 chaperonin gene expression -- Subcellular localization -- Posttranslational modifications -- Variations in Hsp60 and Hsp10 in humans -- Type I chaperonins are essential for cell viability and mutations cause deficiency phenotypes -- Human diseases caused by genetic mutations in the Hsp60/Hsp10 system -- Molecular investigations of disease mechanisms -- Molecular investigations of disease mechanisms -- Outlook.