Thermoplastic polyurethane elastomers (TPUs) are prepared including different amounts of rosin in their composition. Rosin is used either as an additive, mixed in the TPU solutions, or as a reactant in the chain-extension step of polymer synthesis. The properties of the materials are studied using solution viscosity measurements, size-exclusion chromatography, stress-controlled rheometry, differential scanning calorimetry, wide-angle X-ray diffraction, and contact angle determinations. Rosin as an additive does not markedly change the polymer properties. On the contrary, the use of rosin in the chain-extension step leads to sharp increases of viscosity and molar mass as well as improvements of rheological properties and changes in morphology: the crystalline regions are more affected (variations in the softening temperature and enthalpy) than the amorphous ones (quite constant glass-transition temperature). The conclusion is that rosin acts as an actual chain extender and that it modifies the organization of both the hard and the soft segments of the polymers. Furthermore, the TPUs are used as raw materials of solvent-based adhesives, which adhesion properties are characterized by T-peel tests of PVC/TPU adhesive joints. Rosin as an additive cannot improve the low tack (initial adhesive strength) of TPU, although as a chain extender or cochain extender (together with butane diol) rosin allows development of significant initial adhesive strengths, while keeping a high level of actual (maximal) adhesive strength.