- "When the people forget their duty they are no longer human and become something less than beasts. They have no place in the bosom of humanity nor in the heart of the Emperor. Let them die and be forever forgotten."
- — From Prime Edicts of the Holy Synod of the Adeptus Ministorum
The Holy Synod, also known as the Holy Synod of Terra, is the ruling council of the Adeptus Ministorum, also known as the Ecclesiarchy. The Holy Synod is currently based within the Ecclesiarchal Palace on Terra, but at various times in the Imperium's long and tumultuous history, has also been based on Ophelia VII, a world in the Segmentum Tempestus, and one of the richest in the Imperium after Terra and Mars. The Holy Synod is led by the Ecclesiarch, the High Priest of the Imperial Cult, and is comprised of all the Cardinals of the Ministorum, each of whom governs a diocese of the Imperium of Man which can vary greatly in size and astrogeographic scope. The Holy Synod not only acts as the governing body of the Adeptus Ministorum, but it is also the final authority in all matters of religious doctrine for the faith of the Imperial Cult. The Holy Synod was created by the reforming Ecclesiarch Sebastian Thor in the early 36th Millennium to serve as a check upon the power of the Ecclesiarch. This was needed due to the actions of the renegade High Lord of Terra Goge Vandire, who as Master of the Administratum and Ecclesiarch had manipulated the religious faith of the Imperium to achieve political ends in the early 36th Millennium during the period of civil strife in the Age of Apostasy known as the Reign of Blood. The existence of the Holy Synod and its subsidiary organisation, the Synod Ministra, ensures that never again will a High Lord or an Ecclesiarch have total power over the Ecclesiarchy and the powerful state religion of the Imperium.
The Holy Synod periodically holds Ecclesiastical Conclaves in which Cardinals from all over the Imperium journey to Terra and discuss those issues of the day currently most important to the Ecclesiarchy. As the Holy Synod determines religious policy in the Imperium it is extremely influential in the Imperial government and one or more of the Cardinals sitting on the Holy Synod may represent the Synod on the Senatorum Imperialis alongside the Ecclesiarch at different times in Imperial history, especially when the reigning Ecclesiarch is politically weak.
Alongside the Holy Synod based on Terra, another Ecclesiarchy ruling body known as the Synod Ministra exists on the Cardinal World of Ophelia VII. Although the Holy Synod on Terra remains the supreme governing body of the Ecclesiarchy and the primary authority on the spiritual doctrines of the Imperial Cult, the Synod Ministra acts as a secondary governing body. and an alternative source of political power. Located further from Terra, the Synod Ministra relays and disseminates the dictates of the Holy Synod, enforcing the religious laws of the Ecclesiarchy and the Imperium. Secondly, the Synod Ministra provides a defence against the political manipulation of the Ecclesiarchy by other Imperial Adepta based on Terra such as the Administratum or even a single individual within the ranks of the Adeptus Ministorum itself.
- Codex: Sisters of Battle (2nd Edition), pg. 16
- Dark Heresy: Blood of Martyrs (RPG), pp. 9, 11-13, 15, 17, 19, 42