A laser flash photolysis-resonance fluorescence technique has been employed to determine absolute rate coefficients for the CH3F + Cl reaction in N2 bath gas in the temperature range of 200-700 K and pressure range of 33-133 hPa. The data were fitted to a modified Arrhenius expression k(T) ) 1.14 × 10-12 × (T/ 298)2.26 exp{-313/T}. The OH and Cl reaction rates of 13CH3F and CD3F have been measured by long-path FTIR spectroscopy relative to CH3F at 298 ( 2 K and 1013 ( 10 hPa in purified air. The FTIR spectra were fitted using a nonlinear least-squares spectral fitting method including line data from the HITRAN database and measured infrared spectra as references. The relative reaction rates defined by R ) klight/kheavy were determined to be kOH+CH3F/kOH+CD3F ) 4.067 ( 0.018, kOH+CH3F/kOH+13CH3F ) 1.067 ( 0.006, kCl+CH3F/kCl+CD3F ) 5.11 ( 0.07, and kCl+CH3F/kCl+13CH3F ) 1.016 ( 0.006. The carbon-13 and deuterium kinetic isotope effects in the OH and Cl reactions of CH3F have been further investigated by quantum chemistry methods and variational transition state theory.