Natural organic matter (OM) is widespread in terrestrial ecosystems and it plays a major role in the global carbon cycle. Despite this high environmental importance, its characterization at the molecular level remains unsatisfactory, especially when the macromolecular OM is concerned. Such a characterization is challenging because of the diversity and heterogeneity of OM, but it is of prime importance to derive OM reactivity and, more generally, to model environmental processes in which natural OM is involved. This awareness led to a wealth of analytical developments, which are described in the present review. They include improvements of existing techniques, but also new approaches and concern spectroscopic tools along with chemical and thermal degradations.