The Order of the Holy Trinity for the Redemption of the Captives or Order of the Holy Trinity for short (Latin: Ordo Sanctissimae Trinitatis redemptionis captivorum, Ordo Sanctissimae Trinitatis, also known as Trinitarians) is a Catholic religious order that was founded in the area of Cerfroid, some 80 km northeast of Paris, at the end of the twelfth century. The founder was St. John de Matha, whose feast day is celebrated on 17 December. From the very outset, a special dedication to the mystery of the Holy Trinity has been a constitutive element of the Order's life. The founding-intention for the Order was the ransom of Christians held captive by non-Christians, a consequence of crusading and pirating along the Mediterranean coast of Europe. The Order has the initials "O.SS.T." The Order’s distinctive cross of red and blue can be traced to its beginnings.
Between the eighth and the fifteenth centuries medieval Europe was in a state of ongoing war with the expanding Moslem world. Christians took up arms to defend against the advance of Mohammed’s disciples. Arabs successfully managed to subjugate North Africa, most of Spain, Southern France and took over Sicily making the Mediterranean, previously a Roman lake, now a Moslem one. In Christian lands, in the daily conflicts of this secular struggle, Saracens plundered all that could be transported: animals, provisions, fabrics, precious metals, money and especially men, women and children who would be sold for a good price. Privateering and piracy on the Mediterranean sea were aggressive and violent means used by Moslems to harass their Christian enemies and, above all, to obtain large profits and easy gains. For over six hundred years, these constant armed confrontations produced numerous war prisoners on both sides. Islam’s captives were reduced to the state of slaves since they were war booty and submitted to the absolute dominion of their Moorish owners. Such was the condition of countless Christians in the Southern European countries.
The threat of capture, whether by pirates or coastal raiders, or during one of the region's intermittent wars, was not a new but rather a continuing threat to the residents of Catalonia, Languedoc, and the other coastal provinces of medieval Christian Europe.
The redemption of captives is listed among the corporal works of mercy. The period of the Crusades, when so many Christians were in danger of falling into the hands of non-Christians, witnessed the rise of religious orders vowed exclusively to this pious work. 
Pope Innocent III granted the order and its rule approval with his letter Operante divine dispositionis clementia, issued on 17 December 1198. Soon after papal approbation, the Trinitarian ministry to Christian captives was incorporated into the Order's title: Order of the Holy Trinity for the Ransom of Captives. In addition to the Order's purpose of ransoming Christian captives, each local community of Trinitarians served the people of its area. And so, their ministry included: hospitality, care of the sick and poor, churches, education, etc. Eventually, the Trinitarians also assumed the work of evangelization.
Brother John's founding intention expanded quickly beyond the three initial foundations (Cerfroid, Planels, Bourg-la-Reine) into a considerable network of houses committed to the ransom of Christian captives and the works of mercy conducted in their locales. Trinitrian tradition considers St. Felix of Valois cofounder of the Order and companion of John of Matha at Cerfroid, near Paris. In Cerfroid the first Trinitarian community was established and it is considered the mother house of the whole Order.
The first generation of Trinitarians could count some fifty foundations. In northern France, the Trinitarians were known as “Mathurins” because they were based in the church of Saint-Mathurin in Paris from 1228 onwards. Ransoming captives required economic resources. Fundraising and economic expertise constituted important aspects of the Order's life. The Rule's requirement of "the tertia pars" -- that one-third of all income to be set aside for the ransom of Christian captives—became a noted characteristic of the Order.
St. Louis installed a house of their order in his château of Fontainebleu. He chose Trinitarians as his chaplains, and was accompanied by them on his crusades.
Throughout the centuries, the Trinitarian Rule underwent several revisions, notably in 1267 and in 1631. It has been complemented by statutes and constitutions. The thirteenth century was a time of vitality, whereas the following centuries brought periods of difficulty and even decline in some areas. The Council of Trent (1545–1563) was a major turning-point in the life of the Church. Its twenty-fifth session dealt with regulars and nuns and the reform of religious orders. Reforming interests and energies manifested themselves among Trinitarians in France with the foundation at Pontoise, north of Paris, during the last quarter of the sixteenth century. Reform-minded Trinitarians in Spain first established the movement known as the Recollection and then, under the leadership of St. John Baptist of the Conception, a movement at Valdepeñas (Ciudad Real) known as the Spanish Discalced Trinitarians at the very end of the sixteenth century. Far-reaching periods of growth and development followed this rebirth.
In succeeding centuries, European events such as revolution, governmental suppression and civil war had very serious consequences for the Trinitarian Order and it declined significantly. During the last decades of the nineteenth century, the Trinitarians began to grow slowly in Italy and Spain. Its members dedicated themselves to fostering and promoting devotion to the Holy Trinity, evangelising non-Christians, assisting immigrants, educating the young and to becoming involved in parishes. Today the Trinitarian Family is composed of priests, brothers, women (enclosed nuns and active sisters) as well as committed laity. They are distinguished by the cross of red and blue which dates from the origins of the Order. Trinitarians are found throughout Europe and in the Americas as well as in Africa, India, Korea and the Philippines.
Since along with the Order’s mission of ransoming Christian captives, each Trinitarian Community served the people of its area by performing works of mercy, redemption and mercy are at the center of the Trinitarian charism.
Our Lady of Good Remedy 
Our Lady of good Remedy is the patroness of the Order of the Most Holy Trinity. Devotion to Mary under this ancient title is widely known in Europe and Latin America. Her feast day is celebrated on October 8.
See also 
- DeMatha Catholic High School, the only college preparatory and secondary educational school in the Americas run by the Trinitarian Order.
- San Tommaso in Formis, the Trinitarian church in Rome.
- Scapular of the Most Blessed Trinity
- "About the Trinitarians"
- Order of the Blessed Virgin of Mercy
- Brodman, James William, Ransoming Captives in Crusader Spain:The Order of Merced on the Christian-Islamic Frontier, 1986]
- Moeller, Charles. "Order of Trinitarians." The Catholic Encyclopedia. Vol. 15. New York: Robert Appleton Company, 1912. 22 Feb. 2013
- Order of the Most Holy Trinity
- Alban Butler, Paul Burns, Butler's Lives of the Saints (Continuum International Publishing Group, 2000), 5.
- Our Lady of Good Remedy
|Wikimedia Commons has media related to: Trinitarian Order|
- Letter Of Pope John Paul II To The Minister General Of The Order Of The Most Holy Trinity
- Trintarian Official site
- Trinitarian Order
- Trinitarian History
- Adare Trinitarian church