Book excerpt: Marine biological science is now studied at the molecular level and although research scientists depend on information gained using molecular techniques, there is no book explaining the philosophy of this approach. Molecular Approaches to the Study of the Ocean introduces the reasons why molecular technology is such a powerful tool in the study of the oceans, describing the types of techniques that can be used, why they are useful and gives examples of their application. Molecular biological techniques allow phylogenetic relationships to be explored in a manner that no macroscopic method can; although the book deals with organisms near the base of the marine food web, the ideas can be used in studies of macroorganisms as well as those in freshwater environments.