Though the term Adoptionism has been applied to earlier divergent theologies, such as that of Theodotus in the second century, the Hispanic controversy of the same name is an unrelated development. In this case, it refers to a christological debate arguing whether Christ in human form was the divine Son of God by nature or by adoption. The historical record of Adoptionism in Spain is relatively short, lasting only a few decades and beginning in the 780's. It is at that time when the documents of Pope Hadrian I (d. 795) and Elipandus (c. 716-c.805), Archbishop of Toledo, first provide evidence of a new sect led by a man named Migetius. We do not know what, if any, position Migetius held in the Spanish church. However, we do know that neither the Pope nor the Archbishop of Toledo approved of his teachings. In a letter addressed to "all orthodox bishops" in Spain, Pope Hadrian I alerts the Spanish bishops to the flawed doctrine of a certain itinerant bishop named Eliga. He clarifies that the bishop is now a follower of a certain "Mingentius," whom scholars have identified as Migetius. Unfortunately, Hadrian says nothing else about Migetius. In fact, we know very little about him. None of his own correspondence or treatises survive. However, several letters written by Archbishop Elipandus attest to a heated debate transpiring between the two men. The debate stemmed from what Elipandus viewed as misinterpretations Migetius made regarding the Trinity. In one letter, addressed to Migetius himself, the Archbishop accuses Migetius of making grave theological errors and dismisses his ideas as both absurd and laughable. Elipandus analyzed and refuted Migetius. In doing so, the Archbishop revealed his own unorthodox explanation of the nature of Christ. How ever laughable Migetius's purported theories may have been, in his attempt to censure Migetius, Elipandus suddenly found himself at the center of a new controversy.

The see of Toledo was preeminent in the days of Visigothic rule. In the eighth century its prestige remained. As Archbishop of Toledo, Elipandus thus had a certain responsibility to root out heresy in order to maintain orthodoxy within his jurisdiction. Although a sect identified with Migetius persisted until at least the mid-ninth century, Elipandus perceived that he had triumphed in this case. He proclaimed as much in a letter to a certain Abbot Fidelis, who resided in Asturias, a Christian kingdom in northern Spain. The letter was written not specifically in boast of his achievement, but rather was an attempt to entreat the abbot to act against another supposed heretic and threat to the Christian church, a monk known as Beatus of Liébana. Though neither Beatus nor Elipandus make clear when their debate began, according to Beatus, his attention was drawn to Elipandus's letter to Fidelis in 785. At that time, Elipandus accused Beatus and his associate, Etherius, the Bishop of Osma, of confusing the nature of Christ. Furthermore he threatened to banish Beatus and his followers for refusing to profess that Jesus is "adoptive in his humanity, but in no way adoptive in his divinity." Immediately thereafter, in defense of himself and in response to what he concluded were Elipandus's own theological errors, Beatus composed a letter, co-authored by Etherius, that redirected the charge of heretic toward the archbishop himself. Their letter takes the form of a lengthy theological treatise rejecting Elipandus's interpretation and arguing that despite Christ's unique nature, he is the proper son of God, not an adopted son. To Beatus, Elipandus's Adoptionist terminology was an aberration of a principle article of Christian theology.

Two camps began forming within Spain, one pro-Adoption and one anti-Adoption. Within just a few years, the debate also reached beyond the borders of Al-Andalus and Asturias. High in the Pyrennes, in a region just recently under Charlemagne's control, Elipandus found an energetic and well-established supporter, Felix (d. 818), the Bishop of Urgel. Through Felix, Adoptionist theology spread rapidly and allegedly found followers as far west as Germany. Just as quickly however, Elipandus and Felix fell under attack. In 792, Charlemagne called an assembly at Regensburg where Felix and Adoptionism were condemned. Felix recanted, but was sent to Rome to testify in front of Pope Hadrian. There he was imprisoned until he managed to escape and return to Spain the following year. In defense of his ally, Elipandus attempted to redeem Felix by sending a letter directly to Charlemagne, begging that the bishop's honor be restored. Additionally, the archbishop wanted to clear his own name and substantiate his Adoptionist tenets. He wrote a letter to the bishops of Francia seeking to clarify his beliefs and to prove the orthodoxy of his doctrine. His effort was unsuccessful however and his explanation only met with further criticism, particularly from Pope Hadrian. Years earlier when he had had written to the bishops of Spain in 785, Hadrian had received reports from his advisors concerning the situation in Spain. In his letter to the bishops, he commented that he knew Elipandus was confessing the adoption of Christ. At that time, the fact disturbed him, but did not incite him to condemn the archbishop. But after Elipandus sent his letter to the bishops, the Pope received a copy. Now able to analyze the archbishop's christological terminology himself, Hadrian responded with a second letter to the bishops of Spain. Despite Elipandus's quotations from scripture and the doctrine of respected Church Fathers such as Jerome and Augustine, Hadrian charged that the christology was blasphemous and shameful. Two years later at the Council of Frankfurt, Elipandus and Felix found themselves condemned a second time by an assembly which included Charlemagne and legates of the pope, as well as Frankish, Italian, and English bishops. As a result of the council, two proclamations were issued against Adoptionism. The prominent theologian, Paulinus of Aquileia (c. 726-802), authored the first and Charlemagne's advisor, Alcuin of York (c. 734-804), authored the second. Alcuin denounced Adoptionism as a resurgence of Nestorianism, a christology of Greek origin that had long since been refuted by the Council of Ephesus in 431.

Despite the condemnations, Felix and Elipandus remained in their appointments as bishop and archbishop. However after his appointment as abbot of the monastery of St. Martin of Tours in 796, Alcuin found a Latin translation of the Council of Ephesus in the monastery library. The acts gave him the theological tools to produce both an anti-Adoptionist letter to Felix and a longer treatise against him. The bishop responded to Alcuin's polemic with a letter, which again attempted to provide an explanation and defense of his theology. But according to Alcuin, Felix's justification only proved to trouble the abbot further. The terminology seemed to indicate that Felix was not only preaching that Christ was God by adoption, but that Christ was God in name alone. As a result of this even greater blasphemy, Alcuin invited Felix to come to the Council at Aachen and debate the matter in person. The bishop accepted. After a week of arguing, Felix retracted his Adoptionist terminology and recanted for the a second time. Despite his renouncement, the bishop was deposed and his formal confession was sent to his bishopric in Urgel. That same year, Pope Leo III also condemned the Spanish heresy at the Council of Rome. Officially a danger to Frankish orthodoxy, Felix was not allowed to return to Spain and spent the rest of his life living under protective custody in Lyon.

Elipandus died in the early ninth century. By that time Alcuin had produced a second treatise against Felix, a lengthy work filling seven books known as Contra Felicem Urgellitanum Libri VII, and a treatise against Elipandus. To these works a final rebuttal to the Spanish heretics was added after Felix's death in 818. Confined in Lyons, Felix had fallen into relative obscurity. His small following there alarmed Abogard, the Bishop of Lyon. After Felix's death, Abogard discovered another monograph written by Felix rationalizing Adoptionist theology. Alarmed that the heresy may infiltrate his bishopric, Abogard destroyed the manuscript and issued a final confutation, Adversum dogma Felicis Urgellensis. With this work, the debate against Adoptionism came to a conclusion. Though the controversy was short-lived, the formal responses of the Church provided a valuable opportunity for the defenders of orthodoxy. The exchange between the Spanish frontier and the Carolingian Church gave early medieval theologians cause to scrutinize orthodoxy doctrine and to exercise their ability to justify orthodox beliefs through reason. Owing to this initial development of models for the refutation of heterodoxy, the Church was better prepared to answer a sudden abundance of heresies in the later Middle Ages.