The accumulation of organic matter allows inferences about a wide selection of processes in the geological past. The Kimmeridge Clay Formation (Yorkshire, UK) can be regarded as a model of the formation of hydrocarbon source rocks. The driving force of organic matter accumulation is the organic phytoplankton productivity, whereas oxygenation conditions seem to have played a secondary role. In Lake Bouchet (French Massif Central) organic matter appears to be a good indicator of paleoenvironmental changes occurring for over 350,000 years. The book should be of interest to geologists and geochemists interested in organic matter accumulation.