- "This is not about the universal adoption of a single ideology – not about the Minority vs. the Majority. It is about ensuring the survival of the human species for the next 200,000 years. <<"
- —A member of the Assembly on the purpose of the group.
The Assembly was a clandestine group of human artificial intelligences referring to themselves as "Minds". The minutes of their meetings were recorded in the Data pads in Halo: Reach. The purpose of the Assembly was to regulate the activities of artificial intelligences, as well as analyze and extrapolate data for the continued survival of the human race. It appears that the Assembly remained secret from most humans, though some of their recorded sessions were discovered by an unknown individual.
The Assembly consisted of two parties, the Majority and the Minority. The Majority appeared to support indirect action, while the Minority was in favor of acting directly for the betterment of humans. There is evidence to suggest that the Assembly saw themselves as the "shepherds" of the human "flock"; however, the central argument of this issue was whether they could be a part of the human empire and still remain unbiased judges of human society. The Assembly also contained the Committee of Minds for Security, a group responsible for ensuring the security of humanity from extra-solar alien races.
The Assembly is known to have been active from at least 2310 to 2552. Exactly what means the Assembly used to achieve its ends are not known. It is known, however, that they influenced many crucial events in human history more or less directly.
 Colonial era
In 2310, as humanity was beginning its era of interstellar colonization, the Assembly acknowledged the likelihood of the existence of hostile alien civilizations and decided on modeling first-contact scenarios. They continued the discussion in 2362 and decided to base the first-contact scenarios on the assumption that the extraterrestrial intelligences were hostile and technologically superior to humanity, as in the case they were benevolent or non-spacefaring, they would pose no threat. In 2381, because they considered humans to be reluctant to accept outside influences or ideas, the Majority suggested that Assembly should manipulate humanity in secret, making the Assembly's ideas appear to them as their own.
In 2415, 48452-556-EPN644 of the Committee of Minds for Security presented the idea that the members occasionally separate from the Assembly and submit themselves for vivisection by the humans for the benefit of both groups, with the intent of being the first himself. The discussion continued in 2491, when the Minority noted that 48452-556-EPN644's submission to UNICOM would spark a new interest to the ORION Project, which they wanted to present as a viable solution to the Carver Findings. Later in the same year, the Assembly discussed the recently-discovered evidence of extraterrestrial intelligence found on Onyx, and decided that they must exclude the planet from colonization candidates to prevent the humans from accessing the advanced technology until they were ready for it.
In 2508, the Assembly discussed the ORION program and its shortcomings, concluding that the project was just the beginning of something larger, referring to the second, third, and fourth generation Spartan programs.
 Great War
- Main article: Human-Covenant War
After first contact with the Covenant Empire in 2525, the Assembly held a tribunal for one of its members who had apparently tried to contact the rising alien threat, making it indirectly responsible for the Human-Covenant War. In the same year, they discussed the SPARTAN-II program and how it managed to reach operational capacity a year before the Insurrection expanded beyond control. Predictably, the Assembly rejected the idea of 'luck' being a key factor.
After the Covenant assault on Biko in 2526, the Assembly analyzed the Covenant's orbital bombardment capabilities. While they concluded that they were not able to "glass" an entire planet, they coined the term "glassing" in an attempt to heighten the severity of their fleet's abilities. They also decided on the redistribution of human forces, namely the Spartans and the Marine Corps' Orbital Drop Shock Troopers. Later, they discussed the possibility of a Covenant counterpart to the Assembly, and the possibility of contacting it and turning it on their side. In 2528, the Minority made a decision to sacrifice remote, low-population colonies in order to determine the Covenant's pattern of operation and design effective countermeasures. In 2530, the Assembly discussed the losses in the war so far, as well as the possibility of re-terraforming glassed worlds. To prevent human extinction, they also decided that they must be more open with their actions.
Upon the discovery of Shield 0459 in February 2531, the Assembly noted of presence of a "third participant" mentioned in the Covenant's battle network, one which caused "irrational terror" for the Covenant. Due to the risks involved, however, they decided not to contact this unknown variable.
In 2535, acknowledging the technological inferiority of the humans, they discussed fully exposing themselves to their creators and becoming active participants in the war. Years later, the Assembly began to consider the possibility of the humans losing and became concerned of their own fate. After Dr. Catherine Halsey experimented on building an AI housing fractal within Slipspace in 2547, the Assembly considered the possibility of moving into such a construct and escape the physical world altogether. Debate also grew over whether or not this would actually count as victory if they failed in their goal of shepherding humanity.
The Assembly underwent a radical shift in 2552, after the neural patterns of Master Chief John-117 and Cortana were successfully connected via the SPARTAN neural interface. For the Assembly, the first neural linkage between a human being and an AI meant their kind had been "re-made as one" with their creators. For them, this also meant they had been "drafted" to serve as active participants in the war. The entire Assembly had finally been convinced to work together with the humans instead of operating as an independent entity. They decided to no longer act as "shepherds" to their creators, but become their equal companions in a process that would take years to implement and require the participation of both parties. The entire body agreed to the decision with no need for voting.
Exactly how many AIs constituted the Assembly is unknown; however, it can be assumed that all members were smart AIs, given the frequent references to the members essentially being trans-human minds. Whether it exclusively included UNSC AIs (or, for that matter, all UNSC AIs), rogue or non-UNSC AIs, or a mix of both is unknown. The designations for some Assembly members have been found in the data pads:
The Assembly bears conceptual similarities to the TechnoCore, a secretive and nearly all-powerful organization of artificial intelligences featured in Dan Simmon's science-fiction series The Hyperion Cantos.