The American Journal of Psychology (AJP) was founded in 1887 by G. Stanley Hall during what Edwin G. Boring (1950) called the Period of Mental Chronometry and, consistent with the prevailing interests of the time, featured articles of relevance to scientists in this research domain. Contained in the early volumes of AJP were several articles that examined what have become some of the enduring issues faced by researchers studying the structure and timing of mental processing using reaction time (RT) procedures. Collectively, RT research published in AJP during its early years contributed to establishing mental chronometry as an important subfield of psychology. From 1900 to 1950 interest in mental chronometry waned, during what has been called its Dark Age. Nonetheless, interest in the effects of factors such as age and intelligence on total RT continued unabated. Numerous articles pertinent to these effects appeared in AJP. Finally, with the publication of Neisser’s (1963) seminal work on visual search, AJP played an important role in reviving interest in mental chronometry in the latter half of the 20th century and continues in its 125th year of existence to contribute pertinent articles on contemporary research in mental chronometry.