This book covers the basic structural, thermodynamic and kinetic principles are covered and molecular strategies for the adaptation to high temperatures revealed by structure analysis are delineated. The roles of fluctuations, hydration and internal packing are thoroughly dicussed. Enzymes with a particular industrial importance, the subtilisin-like serine proteases, have been extensively studied by protein engineering. One extensive chapter is devoted to the present state of knowledge concerning structure-function relations and the origin of the their structural stability. Last but not least, computational and experimental approaches for the design of proteins with increased thermal stability based on sequences or 3D structures are present