Measures of unemployment tally people without a job who are looking for one. For measurement purposes, the critical question is what constitutes "looking." This article summarizes how unemployment is measured in the United States and Europe, and describes recent research investigating the permeability of the dividing line between the unemployed and "marginally attached" subgroups of those out of the labor market. A continuum between unemployed and entirely inactive individuals indicates that measures beyond unemployment may be useful in judging the state of the labor market.