A comprehensive study of the kinetics and mechanism for the thermal reduction of NO2 by H-2 has been carried out in the temperature range 602-954 K by pyrolysis/FTIR spectrometry employing different mixtures containing (1) NO2/Ar, (2) NO2/NO/Ar, (3) NO2/H-2/Ar, (4) NO2/H-2/CO/Ar, and (5) NO2/H-2/CO/NO/Ar. The results of kinetic modeling for the data obtained from mixtures 1 and 2 gave the rate constant for the key reaction responsible for NO formation and NO2 decay, 2NO(2) --> 2NO + O-2 (4) : k(4) = 4.16 x 10(12) exp(-13 840/T) cm(3)/(mol s). Combination of our data with those of Rohrig et al. (ref 27) measured at high temperatures in shock waves led to k(4) = (4.51 +/- 0.15) x 10(12) exp[-(13 890 +/- 27)/T] cm(3)/(mol s) for 600 K < T < 1450 K. Kinetic modeling of the measured data from mixtures 3-5 indicated that the existing rate constant for H-2 + NO2 --> HONO + H (-1) was too large; on the other hand, our theoretically predicted rate constant, k(-1) = (1.30 x 10(4))T-2.76 exp(-14 980/T) cm(3)/(mol s), obtained by high-level ab initio MO/TST calculations with a small adjustment for the computed barrier from 32.5 to 33.0 kcal/mol, can quantitatively account for measured concentrations of NOx and COx (in CO-added experiment), x = 1 and 2, and for NO2 decay rates reported earlier by Ashmore and Levitt (ref 22).