The hypothesis that life on earth evolved under thermophilic conditions and then adapted at cooler temperatures is based on the discovery, in the last decade, of organisms growing optimally at temperatures near and above 100 °C, termed “hyperthermophiles,” and on the rooted phylogenetic trees based on 16S rRNA sequences proposed by Woese and colleagues in which all branches leading to hyperthermophiles are short and located at the base of the tree. These observations led to the conclusion that the common ancestor of all extant organisms (cenancestor) was a hyperthermophile. This hypothesis, which implies the fascinating opportunity of studying the origin of life by investigating thermophilic organisms, is still the subject of controversy and debate. In particular, considerable opposition arose to the concept of the hyperthermophilic origin of life and to the interpretation of the phylogenetic and geological data. With this in mind, the collection of papers written by selected speakers from the international workshop Thermophiles: The keys to molecular evolution and the origin of life contributes significantly to the discussion by offering the opinions (some of them in open conflict) of leading protagonists from a range of disciplines. In fact, as the editors correctly point out, the majority of researchers in the thermophile field have backgrounds in biochemistry, microbiology, and genetics, but the views of geochemists, oceanographers, and evolutionists would also be of great interest. With this aim, the book gives an opportunity to readers with different backgrounds to approach such fundamental questions as to how life originated and under what environmental conditions.