We report comprehensive inelastic neutron scattering measurements of the magnetic excitations in the 2Dspin-5/2 Heisenbergantiferromagnet Rb2MnF4 as a function of temperature from deep in the Néel ordered phase up to paramagnetic,0.13<kBT/4JS<1.4. Well-defined spin waves are found for wavevectors larger than the inverse correlation lengthξ−1 for temperatures up to near the Curie–Weiss temperature,ΘCW. For wavevectorssmaller than ξ−1, relaxational dynamics occurs. The observed renormalization of spin wave energies, andevolution of excitation lineshapes, with increasing temperature are quantitatively comparedwith finite-temperature spin wave theory and computer simulations for classical spins.Random phase approximation calculations provide a good description of the lowtemperature renormalization of spin waves. In contrast, lifetime broadening calculatedusing the first Born approximation shows, at best, modest agreement around the zoneboundary at low temperatures. Classical dynamics simulations using an appropriatequantum classical correspondence were found to provide a good description ofthe intermediate and high temperature regimes over all wavevector and energyscales, and the crossover from quantum to classical dynamics observed aroundΘCW/S, wherethe spin S = 5/2. A characterization of the data over the whole wavevector/energy/temperature parameter space is given.In this, T2 behaviour is found to dominate the wavevector and temperature dependence of thelinewidths over a large parameter range, and no evidence of hydrodynamic behaviouror dynamical scaling behaviour found within the accuracy of the datasets. Anefficient and easily implemented classical dynamics methodology is presented thatprovides a practical method for modelling other semiclassical quantum magnets.