This chapter explores the aspects associated to ideal reactors, when they are operated in non-isothermal mode. First, the essential arguments about the kinetics and thermodynamics of chemical reactions in relation to temperature are presented, highlighting how the design equations must be now declined. Then, the thermokinetic maps for irreversible and reversible, endothermic and exothermic reactions are built and commented. For each case, the optimal temperature profiles are discussed. Subsequently, the energy and material balances for adiabatic reactors are illustrated, with details on the optimisation conditions in terms of both temperature profiles and reactor choice. An extensive use of graphical methods complements the theoretical discussion.