The kinetics of cellulose pyrolysis have received considerable attention during the past few decades. Despite intensive study, there remains controversy in the literature even on a topic as basic as the global kinetics of pyrolysis. The reported kinetics have been reconsidered in light of new experimental results that suggest a simple resolution to that part of the controversy concerning the activation energy of pyrolysis. It appears that the reported kinetics are sensitive to the heating rate employed in the experiments used to deduce them. Experiments in which the cellulose is rapidly heated to above 600 K give apparently "low" activation energies, mainly between about 140 and 155 kJ/mol, in the case of the material studied here. This applies to both "isothermal" and high heating rate temperature-ramp experiments. Alternatively, cellulose heated more slowly to temperatures below 600 K appears to lose mass with an activation energy that is about 218 kJ/mol. The mathematical modeling of processes involving pyrolysis of cellulosic materials (e.g., biomass conversion processes, fire phenomena) can be strongly influenced by which kinetics are assumed, since the kinetic constants from one regime will not accurately predict mass loss in the other.