We shall here review several aspects concerning the role played by multibody terms (fundamentally up to three, four, five-body terms) in the behaviour of dense states of matter including crystalline structures, solvent effects, adsorption properties of surfaces, membrane transport and oligomer bound states. These few-body terms are collectively defined as the nonadditive contribution to the energy and often have a crucial, sometimes decisive role in the behaviour of the different physical, chemical or biological systems under study. Furthermore they provide us with a reliable guide (free of the usual pitfalls of the ˝trial and error˝ approach) of how to choose the growing few-body models that lead us to understand the nature of the extended systems, as is exemplified in this review.