The family of hsp70 molecular chaperones plays an essential and diverse role in cellular physiology. Hsp70 proteins appear to elicit their effects by interaction with polypeptides that present domains which exhibit non-native conformations at distinct stages during their life in the cell. Work pertaining to the functions of hsp70 proteins in driving protein translocation across membranes is reviewed herein. Hsp70 proteins function to deliver polypeptides to protein translocation channels, unfold polypeptides during transit across membranes and drive the translocation process. All these reactions are facilitated in an ATP-dependent reaction cycle with the assistance of different partner proteins that modulate the function of hsp70.