The fourth edition of the Dictionary of Occupational Titles (DOT) is potentially a major data resource for sociological analysis. The present paper provides previously unavailable information regarding the production and properties of the DOT data to facilitate assessment of their appropriateness for various research purposes. We describe the data available in the DOT, report on exercises assessing their validity and reliability, consider the desirability of aggregating the data in various ways, present a factor analysis that reduces the 44 characteristics to six factors, compare the third and fourth editions with respect to possible sex bias, and offer a cautionary note regarding the use of successive editions of the DOT to study temporal changes in the American occupational structure.