Conjoiners or the Conjoined (pejoratively referred to by outsiders as spiders) are a faction based around mental augmentation and communication, and the advancement of the human mind. Early experiments by the Conjoiner matriarch Galiana and her group on Mars in the early 22nd century with the uses of technology in augmenting consciousness prompted her to begin experimenting with allowing her subject's implants to communicate — triggering the event known as the Transenlightenment, and the beginnings of the Mother Nest and of the Conjoiners. After losing a war with the remainder of humanity, the first Conjoiners later escape the Solar System with the help of Nevil Clavain and colonise other star systems. They then progress to a technological level considerably ahead of the rest of humanity, although still far behind many alien cultures in nearby space. The Conjoiners function as a single society for centuries, before the events of Redemption Ark result in them splintering into numerous factions and disappearing from the affairs of baseline humanity by the time of Absolution Gap, by which point they are engaged in the war with the Inhibitors. With the "Rise of the Greenfly", other human factions are wiped out, leaving an isolated enclave of Conjoiners as the last humans in the galaxy, along with the Ultranaut Irravel. Even they are forced to flee eventually, as the Greenflies' grip on the galaxy increases.
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. All Conjoiners possess, at the minimum, 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, more modern Conjoiners possessed a cranial crest. 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. Clavain and Khouri joined at older ages than normal, and Clavain would have had early generation implants (though not uniquely so); Skade was trained in isolated operation, and later was supported by the alien construct Mademoiselle.
Although Conjoiners seem monolithic and even like a hive mind to outsiders, they each possess their own varied and distinct personalities and deep divisions of thought and opinion still persist amongst them. 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.
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.