An Arrow-Debreu economy is a general-equilibrium model in which goods are defined not only by what they are, but also by when and in which state of the world they are delivered.
Why this model matters
The Arrow-Debreu framework is central to modern microeconomics because it gives a rigorous way to analyze equilibrium, uncertainty, and welfare. By treating delivery in each future state as a separate contingent commodity, the model shows what fully complete markets would look like.
What “complete markets” means here
If every relevant future contingency has a market price, households and firms can trade state-contingent claims to insure against risk and reallocate consumption across states. That makes the model especially useful for proving the existence of competitive equilibrium and the welfare theorems.
Why economists still use it
Real economies do not have perfectly complete markets, but the model provides a benchmark. It clarifies what happens when complete insurance and perfect trade are possible, which in turn helps economists understand what is lost when markets are incomplete.