The mythology and history shared by many of Alastair Reynolds' books has been called the Revelation Space Universe (RSU). The world gets its name from the first book to feature it, namely Revelation Space.
RSU and space opera:
Reynolds writes space opera, which to me means stories that contrast the heroic individuality of the protagonist against the enormity of space. That "enormity of space" refers not only to the incredible geometrical magnitude of space, but also, in the best spirit of sf, the plethora manifestations of life that are possible within its reaches. While each story within the RSU may only involve a few world systems and only a few historical events, it simultaneously suggests that this story is occurring within the manifold of all stories.
RSU stories achieve this sense of universal variegation in a number of ways. One is by having each (or at least "most") of the societies within the RSU presented as being composed of multitudes of subcultures, factions, cults, and trends. This contrasts the monolithic cultures of, for example, Star Trek (once you've seen one Klingon you've seen them all). RSU stories aren't shy to bask in the complexities of life, although admittedly, they achieve most by alluding and glancing rather than showing in detail. Because of this - that is, because the majority of culture-niches go unpresented - there is always the sense there is more to the background of the RSU and its stories than one could ever know. One gets the feeling that every single possible contortion imaginable has been occupied by a partition of society somewhere, sometime.
I could list here some of the examples of factions and races that are described in RSU stories, but to a certain extent this is misleading. It is not necessarily the particulars that is impressive, but the suggestion that these particulars are mere examples of a unfathomable list. It is this appeal to the sublime - to that which is beyond imagining - which good sf aims for and which the RSU achieves.
...bioengineering and cyborg reshaping had equipped humankind for any possible physical environment. Twenty thousand distinct branches of humanity had returned to alien seas, each adopting different solutions to the problem of aquatic life. Some were still more or less humanoid, but others had sculpted themselves into sleek shark-like things, or dexterous multi-limbed molluscs or hard shelled arthropods. There were thirteen hundred distinct human cultures in the atmospheres of gas giants. Nintey that swam in the metallic hydrogen oceans under those atmospheres. There were vacuum dwellers and star dwellers. There were people who lived in trees, and people who had, by some definition, become trees themselves.Thousandth Night
Strikingly, although this quote is from one of Reynolds' stories, it is not set in RSU. This of course means that it is not too easy to separate discussions of Reynolds' style and motifs and those of RSU specifically. I suspect that most of what I've said above can be applied to any of Reynolds' space operas.
There are certain core elements - historical events and personalities, organizations and species, as well locations and technologies - that appear often enough in RSU stories to serve as anchoring points of commonality.
Places:
The location that is mentioned most in RSU stories is Yellowstone. The planet of Yellowstone, and its surrounding orbital habitats, serve as the nexus and zenith of humanity's technological and cultural achievements. Even stories that aren't set in Yellowstone often find reason to mention it. After all, it is the hub of civilization, making anywhere else seem provincial. It is also the location where many key historical figures originated. Because of the great distances between habitable worlds, and because distance is time, stories that are set away from Yellowstone may have different impressions of it, especially impressions that are long out of date. While some stories may see Yellowstone in its prime - a self-aware golden age - others are set after Yellowstone's great decline, when a terrible plague strikes. This melding plague makes use of the nanotechnology and synthetic biology that underlies Yellowstone's power, turning Yellowstone into a grotesque living parody of its former self.
Factions and races:
Although Yellowstone is human dominated, it contains amongst its diversity various human factions. This includes two sort-of transhumanist factions that commonly appear or are referred to in the RSU: conjoiners and ultras. The former are the product of humanity's early attempt at mental augmentation, a sort of post-singularity culture whose advancements have made them alien to the rest of humanity. As for the ultras, they similarly represent a human group's efforts at augmentation, and are a spacefaring culture noted for their mechanical, electronic, and biological prosthesis and modifications.
Most other factions are based on either ideology or religion, or else are family interests, normally based in Yellowstone. A notable example of the latter being the Sylveste clan, who are often mentioned in the RSU due to their power and historical importance.
The focus of the RSU is on humanity and its variants. Few other species are mentioned, relatively, and some of those are the product of humanity anyway.
Technology:
Due to the time span and multitude of settings that make up RSU, technology can differ greatly between stories. Hence there are great differences between Yellowstone at its apex and a small colony elsewhere. Between these two cases, however, there are points of relative consistency, in particular in the technological manifestations of the ultras that travel between these worlds.
Technologies that commonly appear in RSU include the obligatory space travel tech, here conjoiner drives (made by the conjoiners mentioned above). Another important technology are simulations - AI. These range from, at their lowest, AI's designed to assist in data processing, to fully "person" AIs. These more advanced AIs, called alpha level in RSU stories, can be created by a destructive scan and uploading of a biological individual's brain.
This interest in simulations is an example of a general interest in RSU in the limits of humanity. There is an interest in humans becoming more than human - by biomechanical engineering or software prosthesis - or humans approaching a phenomenon which transcends their capacity of human experience - minds that transcend mind.
RSU fiction:
The RSU was first used as a setting in a short story published in 1990, but is best known for its eponymous first novel of 2000. The novels of RSU are considered to be a series, but are largely independent of each other and are non-chronological. Nonetheless, in my opinion, there is some benefit to starting with the first two novels, as they provide a rich background for the entire RSU and its stories.
SciFiQuest 2011: The Undiscovered Nodegel