textThis dissertation investigates several business cycle relationships when economic agents are heterogeneous. The particular focus is on the interactions between the cross-section of agents and the aggregate state of the economy. The first chapter shows that, when occasionally binding capacity constraints limit the production of heterogeneous firms, demand shocks can endogenously generate a number of important business cycle regularities: recessions are deeper than booms are high, firm-level volatility is countercyclical, the aggregate Solow residual is procyclical and the fiscal multiplier is countercyclical. A baseline calibration of a basic New Keynesian DSGE model with capacity constraints shows that this mechanism can explain more th...