A two- dimensional nonstationary model of a fire spreading across a bed of fuel is proposed, incorporating the effects of wind and slope. The contributions of both radiative and convective preheating ahead of the fire front are included. The radiation impinging on the top of the fuel bed is determined, assuming the flame is a radiant surface. Convective heat transfer in the fuel layer is considered using a simplified description of the flow through the fuel bed. Model predictions are compared to laboratory- scale experiments. Dedicated experiments were carried out for horizontal fire spread in still air across beds of pine needles to measure flame and fire front properties using infrared camera, thermocouples, and heat flux sensors. Experiments conducted under wind and slope conditions are also considered.