A discussion is given of the production of sound by low Mach number turbulent flow over the trailing edge of a serrated airfoil. The airfoil is modeled by a fiat plate set at zero angle of attack to the mean flow, and attention is given to both limiting cases in which the chord of the airfoil is either large or small relative to the characteristic acoustic wavelength; a formula is proposed for interpolating predictions at intermediate frequencies. General arguments are advanced which imply that, for serrations of spanwise wavelength ;t and amplitude h, and at radian frequencies to satisfying toh/U>> 1 (U being the velocity of the main stream), the frequency spectrum of trailing edge noise is reduced relative to that for an unserrated edge by 10Γ loglo{Ch/;t} (dB) when ;t/h ~<4, where the constant C-10. This conclusion is confirmed, and predictions are extended to include larger values of ;t/h, by an approximate analytical treatment of the case involving an edge with sinusoidal serrations, and by use of an empirical model of the turbulent flow. At high frequencies the predicted attenuation is about 1 dB when ;t/h ~-10; at ;t/h = 1 the attenuation is typically 7 or 8 dB. It is argued that, in principle, optimal attentuations should be obtained by use of serrations of sawtooth profile with edges inclined at less than 45 Β° to the direction of the mean flow.