Understanding the mechanisms underlying key carbon cycling processes such as decomposition and humification, and how they respond to disturbances such as forestry and conversion to or from agriculture, has become a major focus of research in ecosystem ecology. 13-C NMR spectroscopy offers direct insight into these processes because it provides information on the chemical structure of natural organic matter, including tissues, plant litter, and soil organic matter. Solid-state NMR has the added advantage of being non-destructive. By comparing samples from controlled or repeated-measures experiments, one can gain insight into structural changes that occur during decomposition or as a result of ecological disturbance. However, 13-C NMR spectra of natural organic matter contain broad, overlapping peaks due to the complexity of the material. Soil spectra often have low signal-to-noise ratios, necessitating long analysis times. Therefore, the cross polarization with magic-angle spinning (CPMAS) method is often the only way to analyze large numbers of samples in a reasonable time. Unfortunately, 13-C CPMAS NMR is not generally quantitative. NMR analyses have been conducted on fresh and decomposing plant tissues, soil organic matter, organic matter extracted from soils, and organic matter isolated from stream water and soil water from the Hubbard Brook Experimental Forest, in New Hampshire. Together these samples provide insight into transformations that occur during decomposition and mobilization.