The principles, properties and applications of autothermal fixed-bed reactor concepts are presented. First we focus on different reactor types for weakly exothermic reactions and discuss their basic behavior, their stability and nonlinear dynamic features. The second part is devoted to the autothermal coupling of endothermic and exothermic reactions. A systematic classification is proposed for the process alternatives developed so far and a simplified model is developed from which basic features of an optimal design can be deduced.