There is voluminous survey evidence identifying which, when, and how individuals contact elected officials, but there is less evidence by way of external validation. The goal in this exploratory article is to investigate and extend the empirical trends in letter writing to the chief executive to validate the causes of political letter writing. Using a longitudinal series of heretofore unutilized data spanning 1953 to 1984 collected at individual presidential archives from President Eisenhower to President Reagan, the author tests competing theories about the causes of political letter writing during the modern presidential era. The findings reveal that exogenous events have the strongest effect, followed by presidential mobilization through speeches. Public approval has mixed effects but is strongest when those individuals most likely to participate approve of the president. These findings can help inform us about trends in participation and the evolving role of the public presidency.