Rate coefficients for the reaction C2H + CH4 --> C2H2 + CH3 and C2H + CD4 --> C2HD + CD3 are measured over the temperature range 154-359 K using transient infrared laser absorption spectroscopy. Ethynyl radicals are produced by pulsed laser photolysis of C2H2 in a variable temperature flow cell, and a tunable color center laser probes the transient removal of C2H (X(2) Sigma(+) (0,0,0)) in absorption. The rate coefficients for the reactions of C2H with CH4 and CD4 both show a positive temperature dependence over the range 154-359 K, which can be expressed as k(CH4) = (1.2 +/- 0.1) x 10(-11) exp[(-491 +/- 12)/T] and k(CD4) = (8.7 +/- 1.8) x 10(-12) exp[(-650 +/- 61)/T] cm(3) molecule(-1) s(-1), respectively. The reaction of C2H + CH4 exhibits a significant kinetic isotope effect at 300 K of k(CH4)/k(CD4) = 2.5 +/- 0.2. Temperature dependent rate constants for C2H + C2H2 were also remeasured over an increased temperature range from 143 to 359 K and found to show a slight negative temperature dependence, which can be expressed as K-C2H2 = 8.6 x 10(-16) T-1.8 exp[(474 +/- 90)/T] cm(3) molecule(-1) s(-1).