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Rate coefficients have been measured for the reaction of CH radicals with formaldehyde, CH2O, over the temperature range of 31–133 K using a pulsed Laval nozzle apparatus combined with pulsed laser photolysis and laser-induced fluorescence spectroscopy. The rate coefficients are very large and display a distinct decrease with decreasing temperature below 70 K, although classical collision rate theory fails to reproduce this temperature dependence. The measured rate coefficients have been parameterized and used as input for astrochemical models for both dark cloud and Asymptotic Giant Branch stellar outflow scenarios. The models predict a distinct change (up to a factor of two) in the abundance of ketene, H2CCO, which is the major expected molecular product of the CH + CH2O reaction. [ABSTRACT FROM AUTHOR]