This paper reviews various situations, in which a chemical reaction promotes the mixing (of reactants and products) in an unstirred reactor. One example is an exothermic chemical reaction, which of course increases the local temperature of an unstirred reacting fluid and hence decreases the density. This can produce natural convection. Thus if the walls of the reactor are cooled, there is often toroidal motion in the reacting mixture and consequently enhanced mixing. Of course, the flow field depends on the shape of vessel, but usually natural convection moves fluid up the middle of the vessel and downwards near the cooler walls. Such convective motion influences, in turn, the temperature field and consequently local rates of reaction and heat release. In a large vessel, the velocities associated with natural convection can be large enough for turbulence to arise and so considerably improve mixing. A second example is so-called "critical mixing": this occurs when a substance is close to its critical point and large fluctuations of density, temperature, concentration, etc., can occur. These fluctuations sometimes lead to intense mixing, likely to develop into turbulence. Similar features are manifested by a continuously stirred tank reactor (CSTR) approaching a bifurcation point (critical chaos), consideration of which requires a review of Russian work on the dynamics of a CSTR. Next, a chemical reaction with several steps might behave chaotically. Chaotic behaviour in time implies the generation of spatial inhomogeneities, which can promote mixing. In contrast to driven mixing or stirring, the scales for this "self-mixing" are, as a rule, much smaller than the reactor. This latter property is important for encouraging mixing. Finally, the important cases of a liquid or fluidised bed being mixed by bubbles produced, e.g. by chemical reaction, is briefly considered. (C) 2011 Elsevier B.V. All rights reserved.