The kinetics of the overall reaction between OH radicals and 2,3-pentanedione (1) were studied using both direct and relative kinetic methods at I laboratory temperature. The low pressure fast discharge flow experiments coupled with resonance fluorescence detection of OH provided the direct rate coefficient of (2.25 +/- 0.44) x 10(-12) cm(3) molecule(-1) s(-1). The relative-rate experiments were carried out both in a collapsible Teflon chamber and a Pyrex reactor in two I laboratories using different reference reactions to provide the rate coefficients of 1.95 +/- 0.27, 1.95 +/- 0.34, and 2.06 +/- 0.34, all given in 10(-12) cm(3) molecule(-1) s(-1). The recommended value is the nonweighted average of the four determinations: k(1) (300 K) = (2.09 +/- 0.38) x 10(-12) cm(3) molecule(-1) s(-1), given with 2 sigma accuracy. Absorption cross sections for 2,3-pentanedione were determined: the spectrum is characterized by two wide absorption bands between 220 and 450 nm. Pulsed laser photolysis at 351 nm was used and the depletion of 2,3-pentanedione (2) was measured by GC to determine the photolysis quantum yield of Phi(2) = 0.11 +/- 0.02(2 sigma) at 300 K and 1000 mbar synthetic air. An upper limit was estimated for the effective quantum yield of 2,3-pentanedione applying fluorescent lamps with peak wavelength of 312 nm. Relationships between molecular structure and OH reactivity, as well as the atmospheric fate of 2,3-pentanedione, have been discussed.