The share of U.S. workers in alternative work arrangements has increased substantially in recent decades. Micro longitudinal analyses show that unemployed workers are much more likely to transition into alternative work arrangements than other workers. Macro time-series evidence shows that weak labor market conditions lead to an increase in non-traditional work. But the estimated magnitudes imply that Great Recession and high unemployment in the 2000s can account for only a modest part of the rise in alternative work. Secular factors associated with rising inequality and technological changes making it easier to contract out work appear to be the driving forces.