Shock waves in norbornene(bicyclo [2,2,1] hept-2-ene, C7HlO)-krypton mixtures have been examined with the laser-schlieren technique over the very wide range of conditions, 542-1480 K, and 34-416 Torr in 0.5%, 2%, and 4% C 7 H lO . The experiments exhibit both vibrational relaxation (542-1480 K) and the retro-Diels-Alder dissociation, norbornene---1,3-cyclopentadiene+ethylene (869-1480 K). Over 869-1304 K, and for pressures below 140 Torr, both relaxation and dissociation are resolved. These experiments provide the first measurements of unimolecular incubation (induction) times for the dissociation of a large polyatomic molecule. The ratio t/7 decreases from ~ 5 to 2 in 900-1300 K. Vibrational relaxation is rapid, 10glO P7 (flS atm) =0.066-6.70/T II3 , with a weak inverse temperature dependence, but is completely consistent with series excitation through the lowest-frequency mode. Dissociation shows very strong unimolecular falloff. A Rice-Ramsperger-Kassel-Marcus (RRKM) model, parametrized to fit the observations (E o =44.2 kcal/mol, (AE)down=280 cm-I ), finds the reaction closer to the low pressure limit ko than to koo for 1400 K and 100 Torr. Earlier work at low temperatures « 750 K) has Ea too low to extrapolate to the present results. Thus a significant increase in E: is indicated over 700-1000 K, suggesting a change in mechanism.