We have employed the laser flash photolysis–resonance fluorescence technique to investigate the gas-phase kinetics of elementary steps in the Br-initiated oxidation of 2,3-dimethyl-2-butene (TME) under atmospheric conditions. At T ≥ 274 K, measured rate coefficients are independent of pressure suggesting hydrogen abstraction as the dominant pathway. The following Arrhenius expression adequately describes all kinetic data at 274 K ≤ T ≤ 420 K: k1a (T ) = (3.84 ± 0.84) × 10−11 exp[(−169 ± 61)/T ] cm3 molecule−1 s−1 (uncertainties are 2σ , precision only). At 203 K ≤ T ≤ 241 K, kinetic evidence for reversible addition, Br + TME ↔ Br−TME (k1b , k−1b ), is observed. Analysis of the approach to equilibrium data allows evaluation of the rate coefficients k1b and k−1b . At atmospheric pressure addition of Br to TME occurs at a near gas kinetic rate. Equilibrium constants are obtained from k1b /k−1b . Combining the experimental results with electronic structure calculations allows third-law analyses of the equilibrium data. The following thermochemical parameters for the addition reaction (1b) at 0 and 298 K are obtained