Ever since the work of Putter and Krogh, our understanding of the importance of dissolved and particulate organic matter (POM) in aquatic systems has been closely linked to the development of methods for the sampling and analysis of these materials. Volatile organic materials are defined by the method by which they are made volatile. The concentration of volatile matter available for analysis can be increased by removing the organic compounds from the headspace by adsorption onto a suitable solid phase such as charcoal. The measurement of volatile organic carbon is constrained by the wide variety of compounds making up this fraction. POM in seawater covers the whole size range from macromolecules to whales. As a matter of convenience we exclude the infrequent large particle by the use of some screening device. POM as defined by sediment traps includes the larger and heavier particles normally missed by water-bottle collection methods.