HSP70 molecular chaperone participate in various cellular processes under normal and stress conditions, including the folding of nascent polypeptides, assembly and disassembly of multimeric protein structures, membrane translocation of secreted proteins and protein degradation. All of these activities rely on the ATP-regulated association of HSP70 with short hydrophobic segments in substrate polypeptides. Significant progress has been made in the understanding of the crystal structure of the C-terminal polypeptide-binding domain and the ATP-dependent mechanisms of HSP70.