Soil and sediment organic matter (SOM) play significant roles in sequestration and bioavailability of contaminants in the environment. In this study, advanced thermo-analytical techniques, including thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), temperature-modulated differential scanning calorimetry (TMDSC), and thermal mechanical analysis (TMA) were applied to 13 organic samples (3 woods, 2 humic acids, 3 kerogens, and 5 black carbons) with different diagenetic and anthropogenic histories. Glass transition temperatures (Tg), marking the transition of a material from glassy state to rubbery state, were identified in most samples. Other thermodynamic properties (i.e., heat capacity change, ΔCP, thermal expansion coefficient, a) associated with glass transitions were characterized. It was also found that carbonaceous SOM (e.g., kerogens, black carbons), in general, display higher Tg than humic-based SOM (e.g., humic acids, fulvic acids) due to higher aromatic character, leading to different SOM macromolecular mobility and sorption/desorption behaviors. Failure to observe Tg in some carbonaceous samples (e.g., select soots) does not imply nonexistence of glass transition behavior in these materials. Instead, these samples may possess transition temperatures beyond our experimental temperature-scanning range and thus require additional research.