Heat shock proteins (hsps) were originally identified as proteins expressed following exposure of cells to environmental stress. Several hsps were subsequently shown to play roles as molecular chaperones in normal intracellular protein folding and targeting events, and to be expressed during discrete periods in the development of several embryonic tissues. However, only recently have studies begun to address the specific developmental consequences of inhibiting hsp expression in order to determine whether these molecular chaperones are required for specific developmental events. These studies have demonstrated hsps as important players in the development of a variety of embryonic and adult tissues. This review summarizes key findings in the expression, function, and regulation of hsps during the development of eukaryotic organisms.