We initiate and study the theory of “real decomposable maps” between real operator systems. Formally, this is new even in the complex case, which hitherto has restricted itself to the case where the systems are complex \(C^*\) -algebras. We investigate how our definition interacts with the existing theory (which it generalizes) and with the complexification. In particular, a surprising term appears in the ‘Jordan decomposition’ of real decomposable maps. This term constitutes a new class of completely bounded maps, a class that also showed up in disguised form in our recent study of real noncommutative (nc) convexity, and whose theory is likely to have applications in that subject. We also check the real case of many important known results related to decomposability, for example results about the weak expectation property or injectivity of von Neumann algebras.
