I present a model where firms decide what types of jobs to create and then search
for suitable workers. When there are few skilled workers and the skilled-unskilled
productivity gap is small, firms create a single type of job and recruit all workers.
An increase in the proportion of skilled workers or skill-biased technical change
can create a qualitative change in the composition of jobs, increasing the demand
for skills, wage inequality, and unemployment. I provide some evidence that there
has been a change in the composition of jobs in the United States during the past