The history of articles in the American Journal of Occupational Therapy and its predecessors reflects trends and changes in professional terminology and the thoughts underlying that terminology. In this study, we investigate use of occupation, activity, and related terms across 9 decades of occupational therapy literature from the 1920s to the 2000s. The literature for 3 years of each of the 9 decades was scanned electronically. A random numbers table was used to equalize the number of words across decades, and a computer search function was used to determine each term’s frequency of use for each decade. Results indicated that the term occupation was widely used in the 1920s but then declined until the 1980s. With a rapid increase in use in the 2000s, the term occupation actually appeared more often than it did in the 1920s. The term activity appeared infrequently in the 1920s but gained popularity from the 1930s to the 1960s. From the 1970s to the 1990s, the use of both terms was quite low. This study shows that basic occupational therapy terminology has fluctuated dramatically over time. Given the essential link between terminology and theory, these changes arguably reflect authors’ and editors’ changing viewpoints on the profession’s fundamental nature.