Locke argued that religious belief ought to be compatible with reason, that no king, prince or magistrate rules legitimately without the consent of the people, and that government has no right to impose religious beliefs or styles of worship on the public. Locke's defense of religious tolerance and freedom of thought was revolutionary in its time. Even today, his letter poses a challenge to religious intolerance, whether state-sponsored or originating from religious dogmatists.

Based on both Locke's original Latin and the seventeenth-century English translation of William Popple, this edition offers a reader-friendly version that remains loyal to the original text. In addition to a forty-page introduction that situates the Letter in its historical and philosophical contexts, this edition includes excerpts from writings on religious toleration by William Penn, Baruch Spinoza, Pierre Bayle, and Samuel von Pufendorf, as well as generous selections from the famous Locke-Proast debates on religious toleration.