Workers' ability to delay retirement depends partly on the demands of their jobs. Matching occupational characteristics from the Occupational Information Network to Current Population Survey respondents, this study finds that 7% of American workers held highly physically demanding jobs in 2006 and 35% held highly cognitively demanding jobs. The share of the workforce in physically demanding jobs fell by about one-sixth between 1971 and 2006, while the share in cognitively demanding jobs increased by more than one-third. The decline in physically demanding occupations will likely improve employment prospects for older adults, but the growth in cognitive demands may limit options for some older workers.