A defining feature of business cycles is the comovement of inputs at the sectoral level with aggregate activity. Standard models cannot account for this phenomenon. This paper develops and estimates a two-sector dynamic general equilibrium model that can account for this key regularity. My model incorporates three shocks to the economy: monetary policy shocks, neutral technology shocks, and embodied technology shocks in the capital-producing sector. The estimated model is able to account for the response of the U.S. economy to all three shocks. Using this model, I argue that the key friction underlying sectoral comovement is rigidity in nominal wages.