Chaperonins are a class of molecular chaperones that assemble into a large 
double ring architecture with each ring constituting seven to nine subunits and 
enclosing a cavity for substrate encapsulation. The well-studied Escherichia 
coli chaperonin GroEL binds non-native substrates and encapsulates them in the 
cavity thereby sequestering the substrates from unfavorable conditions and 
allowing the substrates to fold. Using this mechanism, GroEL assists folding of 
about 10-15 % of cellular proteins. Surprisingly, about 30 % of the bacteria 
express multiple chaperonin genes. The presence of multiple chaperonins raises 
questions on whether they increase general chaperoning ability in the cell or 
have developed specific novel cellular roles. Although the latter view is widely 
supported, evidence for the former is beginning to appear. Some of these 
chaperonins can functionally replace GroEL in E. coli and are generally 
indispensable, while others are ineffective and likewise are dispensable. 
Additionally, moonlighting functions for several chaperonins have been 
demonstrated, indicating a functional diversity among the chaperonins. 
Furthermore, proteomic studies have identified diverse substrate pools for 
multiple chaperonins. We review the current perception on multiple chaperonins 
and their physiological and functional specificities.