After the collapse of communism in Eastern Europe, there is renewed interest in comparative studies of system transformation and revolution. System transformation must be delineated from revolution as an outcome. Revolutionary situations are one independent causal variable, but not a definiens of system transformation. Our definition of system transformation as the substitution of previous fundamental political and economic institutions in a polity by new (or different) political and economic institutions is relatively short and points to several typological cases of system transformation. Our causal model of system transformation amounts to almost twenty causal links that can be sizably reduced into five causal bloc variables: state breakdown, defeat in war and external conquest, economic growth, great power rivalry, and natural catastrophes.