This paper revisits the definition of the knowledge economy (Beck, 1992) and investigates changes in knowledge-based industries between 1991 and 2001. Using the General Educational Development Reasoning (GEDR) scale (1-6), non-farm industries were classified as higher knowledge-based industries (GEDR level ≥ 5). The 2001 U.S. national industry-specific occupational employment and wage estimates data were analyzed to identify knowledge-based industries and compared with the knowledge-based industries identified in 1991. There were 41 knowledge-based industries in 1991. In 2001, knowledge-based industries had increased by 50% to 64. Between 1991 and 2001, 27 of the original industries remained classified as knowledge-based industries, and seven industries became non-knowledge-based industries. In 2001, 37 new industries emerged as knowledge-based industries as a result of an increase in their knowledge ratio. Further, the composition of the knowledge-ratio of industries classified as knowledge-based has changed considerably over the period.