This second volume in the series 'Fundamentals in Organic Geochemistry' focusses on molecular chemical aspects introducing the structural diversity of natural products, their fate in the sedimentary systems and the consequences of the corresponding alterations for geoscientific questions. Organic Geochemistry is a modern scientific subject characterized by a high transdisciplinarity and located at the edge of chemistry, environmental sciences, geology and biology. Therefore, there is a need for a flexible offer of appropriate academic teaching material on an undergraduate level addressed to the variety of students coming originally from different study disciplines. For such a flexible usage this textbook series consists of different volumes with clear defined aspects and with manageable length.