In this paper, I discuss three sets of iron links which I uncover in the data on aggregate U.S.
job and worker flows. Job flows are strongly related to aggregate employment growth, while
worker flows are strongly related to employment growth and the unemployment rate. I show
that a simple business cycle model with heterogeneity and passive on-the-job search can
explain these links, with quits and hires interacting to form a hiring chain. Hires beget quits
through on-the-job search, and quits beget hires to replace quitting workers. High
unemployment crowds out quits, shortens the hiring chain, and results in a higher layoff rate
even when employment is expanding. On the other hand, job flows respond purely to changes
in the cross-sectional distribution of firm growth, which responds to employment growth.