chapter 1 Origins, evolution and the hydrogen biosphere / chapter 2 Biodiversity of hydrogenases / chapter 3 Regulation of hydrogenase gene expression / chapter 4 The assembly line / chapter 5 Hydrogenases and their activities / chapter 6 Molecular architectures / chapter 7 Spectroscopy the functional puzzle / chapter 8 The catalytic machinery / chapter 9 Hydrogenase in biotechnology -- Hydrogen consumption / chapter 10 Producing hydrogen as a fuel