a composition in prose or poetry written in the form of a letter to a particular person or group.

In literature there are two basic traditions of verse epistles, one derived from Horace's Epistles and the other from Ovid's Epistulae heroidum (better known as Heroides). The tradition based on Horace addresses moral and philosophical themes and has been the most popular form since the Renaissance. The form that developed from Ovid deals with romantic and sentimental subjects; it was more popular than the Horatian form during the European Middle Ages. Well-known examples of the Horatian form are the letters of Paul the Apostle (the Pauline epistles incorporated into the Bible), which greatly aided the growth of Christianity into a world religion, and such works as Alexander Pope's “An Epistle to Dr. Arbuthnot.” Other writers who have used the form include Ben Jonson, John Dryden, and William Congreve, as well as W.H. Auden and Louis MacNeice more recently.