Friars are different from monks in that they are called to live the evangelical counsels (vows of poverty, chastity, and obedience) in service to society, rather than through cloisteredasceticism and devotion. Whereas monks live in a self-sufficient community, friars work among laypeople and are supported by donations or other charitable support. Monks or nuns make their vows and commit to a particular community in a particular place. Friars commit to a community spread across a wider geographical area known as a province and so they will typically move around, spending time in different houses of the community within their province.
The Carmelites, founded c. 1155. They are also known as the White Friars because of the white cloak which covers their brown habit. They received papal approval from Honorius III in 1226 and later by Innocent IV in 1247. The Carmelites were founded as a purely contemplative order, but became mendicants in 1245. There are two types of Carmelites, those of the Ancient Observance (O.Carm.) and those of the Discalced Carmelites (O.C.D.), founded by St. Teresa of Ávila in the 16th century.
Conventual Franciscans in their variant grey habits
The Franciscans, founded in 1209. They are also known as the Friars Minor. The Franciscans were founded by St. Francis of Assisi and received oral papal approval by Innocent III in 1209 and formal papal confirmation by Honorius III in 1223. Today the Friars Minor is composed of three branches: the Order of Friars Minor (Brown Franciscans), Order of Friars Minor Capuchin (Brown Friars with long pointed hoods) and the Order of Friars Minor Conventual wearing grey or black habits. In the Franciscan order, a friar may be an ordained priest or a non-ordained brother.
The Dominicans, founded c. 1216. They are also known as the Friar Preachers or the Black Friars from the black mantle (cappa) worn over their white habit. The Dominicans were founded by St. Dominic and received papal approval from Honorius III in 1216 as the Ordo Praedicatorum under the Rule of St. Augustine. They became a mendicant order in 1221.
The Augustinians, founded in 1244 (the "Little Union") and enlarged in 1256 (the Grand Union). They are also known as the Hermits of St. Augustine or the Austin Friars. Their rule is based on the writings of Augustine of Hippo. The Augustinians were assembled from various groups of hermits as a mendicant order by Pope Innocent IV in 1244 (Little Union). Additional groups were added by Alexander IV in 1256 (Grand Union).