Hsp27 is a chaperone of the sHsp (small heat shock protein) group among ubiquitin, α-crystallin,Hsp20 and others. The common functions of sHsps are chaperone activity, thermotolerance, inhibition of apoptosis, regulation of cell development, and?cell differentiation. They also take part in signal transduction. The main function of Hsp27 is to provide thermotolerance in vivo, cytoprotection, and support of cell survival under stress conditions. More specialized functions of Hsp27 are manifold and complex. In vitro it acts as an ATP-independent chaperone by inhibiting protein aggregation and by stabilizing partially denatured proteins, which ensures refolding by the Hsp70-complex. Hsp27 is also involved in the apoptotic signalling pathway. Hsp27 interacts with the outer mitochondrial membranes and interferes with the activation of?cytochrome c/Apaf-1/dATP complex and therefore inhibits the activation of procaspase-9.