Rate coefficients for the IO self-reaction, IO + IO --> products (4), were determined over the range 250-320 K and were found to be independent of temperature with an average value of (9.9 +/- 1.5) x 10(-11) cm(3) molecule(-1) s(-1). Absorption cross sections for the IO radical were measured between 340 and 480 nm. The absorption cross section at the peak of the (4,0) band was determined as a function of temperature. The cross section is essentially independent of temperature with an average value between 373 and 203 K of (3.6 +/- 0.5) x 10(-17) cm(2) molecule(-1). Comparison with previous measurements and a discussion of the atmospheric implications of these results are also presented.