Stressproteinssuchastheheatshockproteins(Hsp)andglucose-regulatedproteins (Grp) are front-line molecules in responses to cellular insult and play key roles in the viability of single cell organisms exposed to environmental stresses. However, the discovery of the roles of Hsp and Grp as molecular chaperones indicates much wider functions in the physiology of cells and organisms. It is now clear that some stress proteins are expressed constitutively and are key mediators of housekeeping protein folding in the day-to-day existence of the cell. The maturation of enzymes, transcriptionfactors,andcellsurfacereceptorsreliesonthesefunctionsofthestress proteins. In addition, the ability of stress proteins to manipulate the structures of target proteins has lent them cell regulatory properties over and above their role in folding the proteome and they play key roles in controlling signal transduction, cell death pathways and transcription. Recently, novel extracellular roles for the Hsp have also emerged as it has become apparent that the Hsp can escape from the cytoplasm of cells and play a signi?cant extracellular role in signaling to neighbor cells and in immunosurveiIlance. As might be expected with such key molecules, dysregulation of Hsp expression over time can lead to disastrous results in terms of the health of the organism. Under-expression of the Hsp is associated with advanced aging and neurodegeneration. Elevated expression is associated with malignant progression. We have aimed in this volume to indicate advances in each oftheseaspectsofstressproteinresearch,withchaptersrangingfrombasicstudies of the role of Hsp in protein folding to reviews examining the breakdown of stress protein regulation in disease. Stuart K.