An experimental and kinetic study of the influence of additives on the selective noncatalytic reduction (SNCR) process is presented. Experiments were performed on a lab-scale reactor suitable to investigate the influence of important operating parameters (flue gas temperature, residence time, amount of reducing agent, initial NOx concentration, etc.) on the SNCR efficiency. Several chemical compounds such as CH4, C2H6, C2H4, C2H2, CH3OH, C2H5OH, and CO, which are usually used in the literature as additives for the SNCR process, have been evaluated. The experimental results prove that the use of such additives allows the NO reduction process to be more efficient at lower temperatures. Furthermore, they induce a downward shift up to more than 100 K of the optimal temperature window for the reduction process. Four detailed kinetic mechanisms available in the literature have been tested to model our experimental results. The one that presents the better agreement between experiment and modeling has been optimized to explain the kinetic influence of the additives on the classical SNCR process. The main reaction pathways involved have been pointed out, illustrating the important role of OH radical.