Review of fundamental concept of and phenomenology of combustion. Singularities in nonlinear problems. Matched asymptotic expansion technique. Large activation energy, Danköhler number and rate ratio asymptotics. Ignition/extinction. Laminar burning velocity. Diffusion flame. Aerodynamic effect. Preferential diffusion, differential diffusion, and heat loss effects. Hydrodynamic and acousticnstabilities. Reduced mechanisms.