Concurrent programming enjoys a proliferation of languages but suffers from the lack of a general method of language comparison. In particular, concurrent (as well as sequential) programming languages can-not be usefully distinguished based on complexity-theoretic considerations, since most of them are Turing-complete. Nevertheless, differences between program-ming languages matter, else we would not have invented so many of them. We develop a general method for comparing concur-rent programming languages based on their algebraic (structural) complexity, and, using this method, achieve separation results among many well-known concurrent languages. The method is not restricted to concurrent languages. It can be used to compare the algebraic complexity of abstract machine models, other families of programming languages, logics, and, more generaly, any family of lan-guages with some syntactic operations and a notion of semantic equivalence. The method can also be used to compare the algebraic complexity of families of opera-tions wit hin a language or across languages. We note that using the method we were able to compare lan-guages and computational models that do not have a common semantic basis.