Eucken is the founder of ordoliberalism and the source of its distinctive claim: that a market economy is a constitutional order requiring construction, not a natural condition that appears when the state withdraws.
The Freiburg school formed in the 1930s and continued through the Nazi period, when Eucken remained in Germany, associated with resistance circles including the Freiburg Circles that drafted plans for a post-Hitler order, and was interrogated after the July 1944 plot. That setting is inseparable from the theory. What he observed was cartelized heavy industry entering a symbiosis with a totalitarian state, each strengthening the other, and the conclusion he drew was that concentrated private economic power converts into political power and cannot be treated as harmless because it is private.
His Foundations of Economics (1940) and the posthumous Principles of Economic Policy set out the framework. Economic policy should be concerned with the order — the rules of the game — rather than with the process, and the state should establish constitutive principles: a functioning price system as the central instrument, monetary stability, open markets, private property, freedom of contract, liability, and constancy of policy. Liability matters especially: whoever takes the profit must bear the loss, or the order corrupts.
The role for the state is therefore large and sharply bounded. It must break cartels and monopolies vigorously, which laissez-faire doctrine had not licensed, and must refuse to intervene in prices and outcomes, which interventionist doctrine demanded. A strong state that is independent of interest groups is a precondition of a free economy rather than a threat to it.
He died in 1950 lecturing in London, before the Wirtschaftswunder proved the point.