Adelphopoiesis, or adelphopoiia from the Greek ἀδελφοποίησις, derived from ἀδελφός (adelphos) "brother" and ποιέω (poieō) "I make", literally "brother-making" is a ceremony practiced historically in some Christian traditions to unite together two people of the same sex (normally men) in church-recognized friendship. Similar blood brotherhood rituals were practiced by other cultures, including American Indians, ancient Chinese as well as Germanic and Scandinavian peoples. Such ceremonies can be found in the history of the Catholic Church up until the 14th century and in the Eastern Orthodox Church up until the 18th century. Documented in Byzantine manuscripts from the ninth to the fifteenth centuries, prayers established participants as "'spiritual brothers' (pneumatikous adelphous) and contained references to sainted pairs, including most notably SS Sergius and Bacchus, who were famous for their friendship."  In the late twentieth century, the defunct Christian tradition gained notoriety as the focus of controversy involving advocates and opponents of secular and religious legalization of homosexual relationships in the West.
Adelphopoiesis in Christian tradition
The Russian polymath scholar, priest, and martyr Pavel Florensky offered a famous description of adelphopoiesis in his monumental 1914 book The Pillar and the Ground of The Truth: An Essay in Orthodox Theodicy in Twelve Letters, which included an early bibliography on the topic. Florensky described traditional Christian friendship, expressed in adelphopoiesis, as "a community molecule [rather than an atomistic individualism], a pair of friends, which is the principle of actions here, just as the family was this kind of molecule for the pagan community," reflecting Christ's words that "wherever two or more of you are gathered in my name, there am I in the midst of thee." Florensky in his theological exegesis of the rite described an overlap of Christian agapic and philic love in adelphopoiesis, but not eros, noting that its ceremonies consisted of prayer, scriptural reading, and ritual that involved partaking in presanctified eucharistic gifts 
Alternative views are that this rite was used in many ways, such as the formation of permanent pacts between leaders of nations or between religious brothers. This was a replacement for "blood-brotherhood" which was forbidden by the church at the time. Others such as Brent Shaw have maintained also that these unions were more akin to "blood-brotherhood" and had no sexual connotation.
Rites for "adelphopoiesis" are contained in Byzantine manuscripts dating from the ninth to the 15th century.
"Same-sex union" or "brother-making"?
The ritual gained popular attention in the West, however, after the late Yale historian John Boswell in his book Same-sex unions in pre-modern Europe, also published as The marriage of likeness, argued that the practice was to unite two persons in a marriage-like union. His theory was disputed by other academics expert on the issue, notably historian Claudia Rapp in a special issue of the Catholic scholarly journal Traditio (vol. 52) in 1997, as well as Byzantine liturgical historian Stefano Parenti, who identified the origins of problems in Boswell's manuscript analysis. Boswell's work also was disputed by the religious community today descended most directly from that involved in the original practice, the Greek Orthodox Church, which regarded his work as a modern American cultural appropriation of its tradition, and translates adelphopoiesis as "fraternization," involving a chaste friendship. A similar translation of the term is "brother-making".
While many scholars criticized Boswell's findings, some agreed with him, including liberal American Episcopalian scholars Robin Scroggs and William L. Countryman. Boswell gave text and translation for a number of versions of the "fraternization" ceremony in Greek, and translation for a number of Slavonic versions (Bratotvorenie), although Rapp and others disputed the accuracy of his translations. Boswell himself denied that adelphopoiesis should be properly translated as "homosexual marriage," but he argued that "brother-making" or "making of brothers" was an "anachronistically literal" translation and proposed "same-sex union" as the preferable rendering. Boswell's preference was problematic to Orthodox canonists, as well as scholars such as Rapp, who argued that it involved an anachronistically modern secular epistemology and anthropology, different from traditional Christianity. Boswell suggested a potential parallel to modern constructions of sexual identity, although the rites for adelphopoiesis explicitly highlighted the spiritual nature of the union in premodern Christian terms.
Boswell commented on the lack of any equivalent in the Western Latin Rite of the Roman Catholic Church, but the British historian Alan Bray in his book The Friend, gave a Latin text and translation of a Latin Catholic Rite from Slovenia, entitled Ordo ad fratres faciendum, literally "Order for the making of brothers". Allan Tulchin, "Same-Sex Couples Creating Households in Old Regime France: The Uses of the Affrèrement." in the Journal of Modern History: September 2007, argued that the ceremony of affrèrement in France joined unrelated same-gender couples in lifelong unions, who then could raise family, hold property jointly, and were in all respects the same as or equivalent to marriages in terms of law and social custom, as shown by parish records. These were not, however, contiguous with the earlier Eastern tradition, and not described in sexual terms in parallel to modern concepts of sexual identity.
Archimandrite Ephrem Lash criticized Boswell's book in the February 1995 issue of Sourozh. According to Ephrem, Boswell mistranslates, misinterprets, and tendentiously organizes texts, and his "knowledge of Orthodox liturgiology is, in effect, non-existent." With regard to Boswell's central claim to have found evidence for the use of wedding crowns in the rite for making brothers, Ephrem notes that what the relevant text says, "somewhat literally translated," is this: "It is inadmissible for a monk to receive [anadochos is a standard Greek word for 'godparent'] children from holy baptism, or to hold marriage crowns or to make brother-makings. 150:124]" In other words, "monks are forbidden to do the following: 1. To act as godfathers at baptisms, 2. To act as supporters of bridal couples, 3. To enter into brotherly unions. These are, of course, the natural consequences of a monk's having given up all ties of earthly relationships." Turning back to Boswell's thesis, Ephrem writes, "What does Boswell make of this? Here is his paraphrase of the text given above: 'monks must also not select boys at baptism and make such unions with them'. There is absolutely nothing in the text to suggest that the three prohibitions are linked in the way Boswell implies, nor that the 'children' are 'boys' – the Greek has the neuter, paidia. In short, this first piece of evidence for the use of crowns in the ceremony of brother-making is not evidence for anything, except Boswell's ignorance, not to mention the prurient suggestion that Byzantine monks went round selecting suitable boys at baptism so as to 'marry' them later on."
In his review of the book, Miodrag Kojadinović says: "The book is a scientific treatise abundant with references. But it starts from a premise that to me seems insufficiently proven. It chooses to see, based on relatively meagre evidence, a very idiosyncratic relationship sanctioned among certain ethnic groups as a precursor to California bunnies' white weddings. It goes so far to refer to the emperor Basil as a 'hunk'. It neglects the fact that adelphopoiesis/pobratimstvo can be achieved through simple invocation: 'My-Brother-Through-God!' in case of peril. A foe suddenly turns an ally." 
- Blood brotherhood
- Law of adoption (Mormonism)
- Platonic love
- Romantic friendship
- Patrick Viscuso, Greek Orthodox canonist. ""Failed Attempt to Rewrite History" New Oxford Book Reviews December 1994". Retrieved 2013-08-04.
- Florensky, The Pillar and Ground of the Truth', translated by Boris Jakim, Princeton 1997, p. 571-72.
- Florensky, The Pillar and the Ground of the Truth, p. 301.
- Florensky, The Pillar and Ground of the Truth', p. 327.
- http://www.eskimo.com/~nickz/qrd-eastern_orthodox/adelphopoiia.some-responses and http://www.melkite.org/Questions/M-4.htm
- Shaw, Brent (July 1994). "A Groom of One's Own?". The New Republic: 43–48. Archived from the original on May 7, 2006. Retrieved June 25, 2009.
- Viscuso, Patrick. "Failed Attempt to Rewrite History", New Oxford Review, December, 1994
- See Parenti's review in Byzantinische Zeitschrift 89: https://www.academia.edu/5791320/J._Boswell_Same-Sex_Unions_in_Premodern_Europe_New_York_1994_in_Byzantinische_Zeitschrift_89_1996_448-449
- Fr. Evangelos K. Mantzouneas, Secretary of the Greek Synod Committee on Legal and Canonical Matters; English translation by Efthimios Mavrogeorgiadis, May 1994;Minor editing by Nicholas Zymaris. "Report on Adelphopoiesis 1982: "Fraternization from a Canonical Perspective" Athens 1982". Retrieved 2009-02-03.
- "Reviewing Boswell". Fordham.edu. Retrieved 2013-12-04.
- Boswell, Same-sex Unions in Pre-Modern Europe, p. 298-299.
- hina genontai pneumatikoi adelphoi hyper tous sarkikous (Boswell translation: "that they be joined together more in spirit than in flesh"). Greek text in Boswell, Same-Sex Unions, p. 316, n. 198.
- Allan Tulchin, "Same-Sex Couples Creating Households in Old Regime France: The Uses of the Affrèrement." Journal of Modern History: September 2007
- Young, Robin Darling (November 1994). "Gay Marriage: Reimagining Church History". First Things 47: 43–48. Retrieved June 25, 2009. participated in a modern Syriac version of an adelphopoiesis ceremony at a Syriac Orthodox (Oriental Orthodox) church, but disputed Boswell's thesis as well: "This is a subject about which I have the good fortune to speak not merely as a scholar or an observer, but as a participant. Nine years ago I was joined in devout sisterhood to another woman, apparently in just such a ceremony as Boswell claims to elucidate in his book. The ceremony took place during a journey to some of the Syrian Christian communities of Turkey and the Middle East, and the other member of this same-sex union was my colleague Professor Susan Ashbrook Harvey of Brown University. During the course of our travels we paid a visit to St. Mark’s Monastery in Jerusalem, the residence of the Syrian Orthodox archbishop. There our host, Archbishop Dionysius Behnam Jajaweh, remarked that since we had survived the rigors of Syria and Eastern Turkey in amicable good humor, we two women must be good friends indeed. Would we like to be joined as sisters the next morning after the bishop’s Sunday liturgy in the Church of the Holy Sepulchre? Intrigued, we agreed, and on a Sunday in late June of 1985, we followed the bishop and a monk through the Old City to a side chapel in the Holy Sepulchre where, according to the Syrian Orthodox, lies the actual tomb of Jesus. After the liturgy, the bishop had us join our right hands together and he wrapped them in a portion of his garment. He pronounced a series of prayers over us, told us that we were united as sisters, and admonished us not to quarrel. Ours was a sisterhood stronger than blood, confirmed in the outpouring of the Holy Spirit, he said, and since it was a spiritual union, it would last beyond the grave. Our friendship has indeed endured and flourished beyond the accidental association of two scholars sharing an interest in the Syriac-speaking Christianity of late antiquity. The blessing of the Syrian Orthodox Church was a precious instance of our participation in the life of an ancient and noble Christian tradition. Although neither of us took the trouble to investigate the subject, each privately assumed that the ritual of that summer was some Christian descendant of an adoption ceremony used by the early church to solemnify a state-that of friendship-which comes highly recommended in the Christian tradition (“Henceforth I call you not servants . . . but I have called you friends.” [John15:15]). If this were all that Professor Boswell were claiming to have “discovered,” neither I nor anyone else would be likely to dispute his findings. It seems reasonable to assume that ceremonies like the one Susan Ashbrook Harvey and I went through continue to take place in those eastern churches that preserve the rite of adoption (adelphopoiesis) for friends. In fact, scholars of the liturgy have known for years of these rituals. But any such modest claim is not what Boswell has in mind. He claims that the “brother/sister-making” rituals found in manuscripts and certain published works are ancient ceremonies whose cryptic (or, in current argot, “encoded”) purpose has been to give ecclesiastical blessing to homosexual or lesbian relationships, thus making them actual nuptial ceremonies. This startling claim is certainly far from the reality of the ceremony in which we participated nine years ago."
- Archimandrite Ephrem, "Review of Same-Sex Unions in Premodern Europe", Sourozh, no. 59 (Feb. 1995): 50–55.
- Patrologiae Graecae 150:124.
- Archimandrite Ephrem, "Review of Same-Sex Unions in Premodern Europe", p. 52.
- Miodrag Kojadinović: Same-Sex Unions in Pre-modern Europe by J.Boswell (book review) — Angles Magazine, Vancouver, August 1994