This chapter presented the reversible architecture of the MiMo2 prototype. The architecture is motivated by considering the `subset problem', as discussed by . The linguistically possible translation relation between two languages is defined by a series of reversible constraint-based grammars. I showed how constraint-based grammars can be used to define transfer rules. By requiring that transfer rules are `compositional' in a certain sense made precise, we showed that grammars can be guaranteed to be reversible. I also showed that certain non-compositional translations can still be handled in the framework I proposed. This motivated the claim that reversible transfer grammars provide an interesting compromise between expressive power and computational feasibility.