It is now well understood that, although proteins fold spontaneously (in a 
thermodynamic sense), many nevertheless require the assistance of helpers called 
molecular chaperones to reach their correct and active folded state in living 
cells. This is because the pathways of protein folding are full of traps for the 
unwary: the forces that drive proteins into their folded states can also drive 
them into insoluble aggregates, and, particularly when cells are stressed, this 
can lead, without prevention or correction, to cell death. The chaperonins are a 
family of molecular chaperones, practically ubiquitous in all living organisms, 
which possess a remarkable structure and mechanism of action. They act as 
nanoboxes in which proteins can fold, isolated from their environment and from 
other partners with which they might, with potentially deleterious consequences, 
interact. The opening and closing of these boxes is timed by the binding and 
hydrolysis of ATP. The chaperonins which are found in bacteria are extremely 
well characterized, and, although those found in archaea (also known as 
thermosomes) and eukaryotes have received less attention, our understanding of 
these proteins is constantly improving. This short review will summarize what we 
know about chaperonin function in the cell from studies on the archaeal 
chaperonins, and show how recent work is improving our understanding of this 
essential class of molecular chaperones.