Conjoiners use technology to create a localised group mind. Individual identities are retained, but the group generally functions as a single unit working harmoniously toward its goals. Conjoiner implants are typically neural, and the basic implant is a net of nanomachines that mimic their host's brain structure and thus augment the host's neural capabilities. Artificial enhancements such as vision overlays are not uncommon, and Conjoiners can communicate neurally through fields generated by their implants, which may or may not be amplified by background systems depending on the situation. Most Conjoiners use only neural communication with other Conjoiners and do not physically speak. Their implants also offer them a host of other abilities, such as the ability to hack into and operate a considerable amount of advanced machinery; they have little trouble overriding most software security protocols save their own, and can reprogram weapons to attack their users. They also typically modify their own bodies (often using muscle fibres based on those of chimpanzees) to make themselves physically stronger. Also, at least by the 26th century, the Conjoiners had decided to introduce the cranial-crest to all of the newly recruited. As well as being aesthetically pleasing, it allows dissipation of the huge amounts of thermal energy their super-charged brains produce.
Conjoiners are typically used to being part of a group mind, and most experience disquiet or worse if cut off from other Conjoiners. The few who are capable of operating by themselves are viewed with ambivalence by the rest of Conjoiner society. Notable individuals with this capability include Clavain, Khouri, Skade, and Remontoire. For some, particularly Clavain, it is suspected that this ability has to do with the outdated technology of his implants, which still persist from the very early days of the Conjoiners. In addition to this, Clavain, Skade and Khouri were all born outside the Conjoiners and joined them later, which may also explain why they can leave the collective at will. (It should be noted that virtually no Conjoiners in the novels are actually affected by leaving the collective mind and rejoining it later).
Conjoiners are famous throughout humanity as the only faction capable of building the starship drives that allow interstellar travel. The drives can provide acceleration without requiring any reactant mass. They typically provide constant acceleration needed to drive a starship up to a sizable fraction of the speed of light, typically at one gee to provide artificial gravity, though they were pushed to several gees in Redemption Ark. This is despite the starships in question being tremendous vessels called "lighthuggers" that are several kilometres long and have carrying capacity for tens of thousands. The drives are tamper-proof (to the extent that unauthorised attempts to open them will cause the entire engine complex to explode with sufficient force to destroy the ship carrying it) and thus no other faction has ever been able to copy the designs. The drives were initially introduced from the perspective of non-conjoiner characters, who do not understand how they might work. Later, an answer was provided in Redemption Ark, the first novel to focus on the perspective of Conjoiner characters, where it was revealed that each of the drives has one end of a stable wormhole fixed to the machinery of the interior, the other end fixed in the quark-gluon soup of the first few minutes of the Universe, so that a stream of quark-gluon soup provides both the energy and the reactant mass to drive the engine. It should be noted, however, that the Conjoiners did not actually invent the drive themselves, but received the instructions for it via the Exordium. In the short story Weather, it is revealed that the drives are stabilised by the use of a heavily augmented Conjoiner brain, which is possibly one of the reasons why other factions in the Revelation Space Universe have had no success at creating similar drives.
Although Conjoiners seem monolithic and even like a hive mind to outsiders, some unusual circumstances can still lead to deep division and struggle among them - which as a prerequisite requires them to mask their thoughts from each other without letting on that they are doing so, a difficult feat. Clavain later tells other characters that each Conjoiner is in fact different and has a different mind as all humans do; normal humans simply cannot see it.
The Conjoiners were first introduced in the short story "The Great Wall of Mars", which was first published in Spectrum SF #1, in February 2000, but republished in the collection of short Novellas, Galactic North (2006). At this point, the Conjoiners lived on Mars and the Transenlightenment was relatively recent. The story includes Nevil Clavain, initially an outsider, meeting Galiana and Remontoire, and then joining the Conjoiners. The Conjoiners are then a mere shadowy background group in the novels Revelation Space (2000) and Chasm City (2001), but are the centre of the short story "Glacial", first published in Spectrum SF #5 in March 2001, again republished in Galactic North (2006), which takes place at humanity's first interstellar colony. The Conjoiners are the central focus of the next novel, Redemption Ark (2002), and feature prominently in the following novel, Absolution Gap (2003).
In the afterword of Galactic North, Alastair Reynolds comments that the Conjoiners are not an entirely new concept, and may owe some of their origin to the Human Hive-mind culture from Michael Swanwick's Vacuum Flowers.
Until the time of the Melding Plague, there were several powerful families within the Demarchy, one of the most influential being House Sylveste which controlled SISS or Sylveste Institute for Shrouder Studies, as well as SIAM or Sylveste Institute for Artificial Mentation (before it was destroyed by Panoply during The Clockmaker incident). It later organized the archaeological expedition to Resurgam. They were immensely wealthy, being the closest thing to royalty in the Yellowstone system. Notable characters from House Sylveste include Dan Sylveste, who led the Resurgam expedition; Calvin Sylveste, who is known for the Eighty.
The Demarchists (particularly the Yellowstone Demarchy) also used to have expertise in nanotechnology, life-extension, and biological alterations, among other things. They also utilised a sophisticated information network known as abstraction. Abstraction was used to simulate environments and co-ordinate servitors and other robots. The height of Demarchist society, the Belle Époque, was only brought low by the Melding Plague, which pushed Chasm City, the main city of the Yellowstone Demarchy, into a Dark Age lasting forty years.
Later, after the Conjoiners stepped in to help revive Chasm City, the Demarchists, unhappy with their new role as second fiddle, declared war on the Conjoiners, a war which first went well as the Conjoiners, thanks to their hive-mind nature, became predictable on the battlefield. The return of the war-hero Clavain ended that, and by the time of the events in the book Redemption Ark only the most partisan of Demarchists would even deny an eventual Conjoiner victory.
Demarchist weaponry, among other things, consists of antimatter munitions (or "pinhead" bombs, called such as the tiny amount of antimatter necessary for such weapons can be stored in minute vessels), typically antilithium, and massive rail guns that accelerate foam-phase metallic hydrogen to a massive speed using a series of timed detonations along a barrel. They also utilise various ionisation-particle weapons and compact "fold-out" beam weapons
The Yellowstone Demarchy is destroyed by the time of Absolution Gap by the Inhibitors. In the afterword of 'Galactic North', Alastair Reynolds comments that the Demarchists are not his own invention. He continues on to credit the Joan D. Vinge book 'The Outcasts of Heaven Belt' as the inspiration for the Demarchist Society.
In Revelation Space, a quirk of Ultra society is described which is not referred to again in subsequent novels set within the same universe; for each session in Reefersleep, they grow and maintain a dreadlock as a badge of their status, although they are also described as using these status symbols as stakes in gambling games, and once again, Ilya Volyova, although an Ultra, does not sport these dreadlocks. Aesthetics do appear to be of greater concern to most Ultras than more pragmatic concerns such as functionality and reliability; the most extensively modified Ultras described in the books have, apparently intentionally, turned themselves into living sculptures.
Unlike other factions in the Revelation Space Universe, such as the Conjoiners and Demarchists, there appears to be no unifying political structure or philosophical school of thought behind Ultra society. Although extremely isolated from baseline humanity (and everyone else not aboard ship) during their long voyages, they do not appear to form particularly close associations even within crews; For the crews of the Nostalgia For Infinity (Revelation Space) and of the Gnostic Ascension (Absolution Gap), power struggles and mistrust are presented as the normal state of affairs. (Although it should be noted that neither crew is exactly normal; shipmaster Inigo Standish in Galactic North comments that Ultras like these crews are a minority).