The National Day of Reason is a secular observance kept in the United States on the first Thursday in May, on which humanist, atheist and secularist groups hold public events, blood drives, food collections and civic ceremonies, and press local and state authorities for proclamations. It was established in 2003 by the American Humanist Association, together with the Washington Area Secular Humanists, and it is deliberately timed to coincide with the National Day of Prayer, which falls on the same day and which its organisers regard as an improper government endorsement of religion in tension with the constitutional separation of church and state.
The day is framed positively, as a celebration of reason, of science, and of the First Amendment's separation of church and state, rather than as an attack on religious belief; its promoters present it as an inclusive alternative for the non-religious and as a defence of secular government, and use it to encourage civic and charitable action. It has no rites of its own, and its observance is a matter of events, statements and advocacy. As a self-consciously oppositional yet constructive observance, the National Day of Reason illustrates how the modern secular movement in the United States has developed its own calendar of days, often defined in relation to the religious observances it seeks to counterbalance.