Molecular chaperones are highly conserved in all free-living organisms. There are many types of chaperones, and most are conveniently grouped into families. Genome sequencing has revealed that many organisms contain multiple members of both the DnaK (Hsp70) family and their partner J-domain protein (JDP) cochaperone, belonging to the DnaJ (Hsp40) family. Escherichia coli K-12 encodes three Hsp70 genes and six JDP genes. The coexistence of these chaperones in the same cytosol suggests that certain chaperone-cochaperone interactions are permitted, and that chaperone tasks and their regulation have become specialized over the course of evolution. Extensive genetic and biochemical analyses have greatly expanded knowledge of chaperone tasking in this organism. In particular, recent advances in structure determination have led to significant insights of the underlying complexities and functional elegance of the Hsp70 chaperone machine.