Implementing at least one endothermic and/or exothermic reaction in a compact reactor which has passages for conducting gaseous and/or liquid media, through which passages the reactants of the endothermic or exothermic reaction as well as a heating medium or coolant are sent, whereby a) The endothermic reaction is implemented in heat exchange with a heating medium, b) The endothermic reaction is implemented in heat exchange with an exothermic reaction, or c) The exothermic reaction is implemented in heat exchange with a coolant. The heat exchange between the media mentioned in a) to c) is carried out indirectly and via a third gaseous and/or liquid medium (moderation medium).