The Dragonmarked Houses are thirteen extended families which control most business throughout Khorvaire. Within the houses, only a small percentage of every generation manifest dragonmarks, which are marks on the body that grant spell-like abilities to those born with them. These dragonmarks are designated by taking the Least, Lesser or Greater Dragonmark feat or taking levels in the Dragonmark Heir prestige class. There used to be thirteen dragonmarks but only twelve remain. Each family possesses only one type of mark, and only one or two races can manifest a particular type of mark. Additionally, only races listed in the Player's Handbook can manifest a dragonmark at all - however, this was revised in the 4th Edition Eberron Player's Guide. With the exception of House Phiarlan and House Thuranni (which both possess the Mark of Shadow), each house exclusively has one type of dragonmark.

Dragonmarks come in five forms: aberrant, least, lesser, greater, and Siberys. Aberrant dragonmarks are deviations from normal marks and are not recognized by the dragonmarked houses. People who have aberrant dragonmarks are commonly believed to have been warped by Khyber, the Dragon Below. Least, lesser, and greater dragonmarks can be gained by taking the appropriate feats or taking levels in the Dragonmark Heir prestige class. These types of marks must be taken in order. The Siberys mark is the greatest mark, but someone cannot have both a least, lesser, or greater mark along with a Siberys mark. A Siberys mark is gained by taking the Heir of Siberys prestige class. In 4th edition, dragonmarks are gained by taking the feat associated with the mark, and its power can be increased by choosing the corresponding dragonmark paragon path.

The number 13 plays an important role in Eberron, particularly in the form of “thirteen minus one”, where a group of 13 lost one of its number, resulting in 12. Some examples are:

• There are 13 outer planes, but only 12 of them orbit the material plane of Eberron.
• There are 13 different dragonmarks (not houses), but only 12 currently exist (all known bearers of the Mark of Death were destroyed). Similarly, there are 13 Dragonmarked Houses, but they only represent these twelve remaining Marks.
• There are currently 13 different nations, but one of those is a wasteland (the Mournland). Not all nations are “officially recognized.”
• The ancient calendar of the giant empire is said to have 13 months, whereas the current calendar has 12.
• During the Age of Giants, legend says there were 13 moons, but currently there are 12 (one has vanished).
• In the dwarven Morin Holds, there were 13 clans, but one has been destroyed, leaving 12.

Note that the number 13 is known as a “baker's dozen.” Because the phrase has an established use it is used as a play on the author's name.

Dragonshards are rock or crystal fragments originating from the three legendary dragons of Eberron's creation myth. The three sections of Eberron's world, Siberys, Eberron and Khyber, each produce a distinct form of dragonshard, with a unique appearance and distinct magic affinity. Dragonshards are among Eberron's most important resources. Their scarcity makes them valuable and a frequent goal of quests

Dragonshards are hard, translucent rock or crystal fragments with swirling, pulsating veins of color suspended within them. The veins have the appearance of dragonmarks. Although dragonshards are translucent, their glowing veins give them a distinctive color and make them look almost alive.

Siberys shards fall from the Ring of Siberys that encircles Eberron. They are usually found in equatorial regions such as Xen'drik. They contain a pulsating swirl of golden veins. Siberys shards are the rarest type of dragonshard, and the type most closely associated with the dragonmarked houses. Because of their scarcity and importance to powerful groups, a new find of Siberys shards is often the focus of intrigue or theft. They are sometimes called sunstones or starmotes, or simply dragonshards, because of their association with the dragonmarked houses. Siberys shard items focus or enhance the power of dragonmarked characters, and can enhance psionic powers. Dragonmarked houses are of central importance to the economy and society of Khorvaire, so their artificers have both the means and the need to develop methods to enhance the power of dragonshards. The resulting proliferation of Siberys shard items range from devices focused on enhancing the power of a specific mark to generalized tools that work for anyone who bears a dragonmark. Kalashtar psions and the Inspired lords of Riedra have found a way to harness the power of Siberys shards by undergoing a painful process that embeds a shard in their body, providing enhanced mental or physical abilities.

Khyber shards are found beneath the earth near layers of magma or sulfur vents, typically growing on volcanic cavern walls. They are found throughout Eberron but are particularly common in areas known for fiendish activity, such as the Demon Wastes. Khyber shards have a smoky appearance, with writhing midnight blue to oily black veins running through them. They are sometimes known as nightshards or demonstones. Khyber shard items have an affinity for binding magic. They are common components of binding diagrams, soul trapping spells and similar magic associated with binding creatures.

Eberron shards are found buried in shallow soil in clusters encased in geodes. They are found only in Khorvaire and Aerenal. Eberron shards have a pinkish appearance and churn with crimson blood-red swirls. They are commonly known as bloodstones. Eberron shard items store magical energy or psionic power as spellbooks, spell-storing items or psionic power stones. Intelligent magical items often incorporate Eberron shards. Their magical affinity is very broad compared to the specific powers of Siberys and Khyber shards. Spellcasters can attune Eberron shards to a specific spell, enhancing the power of that spell when it's cast on the shard, and they can encode their spells in shards instead of scribing them.

Dragonshards can be crafted to power magic items, artefacts and constructs, or to augment dragonmark abilities. Dragonshard items vary in power depending on the purity of the dragonshard used. They are rarely large enough to craft into items of significant size; most often, small dragonshards are formed into jewellery. Larger dragonshards, up to the size of a fist, can be crafted into larger focus items.

Dhakaan was an ancient goblinoid empire that dominated the continent of Khorvaire, until the coming of the extraplanar Daelkyr 16,000 years ago. The Dhakaani goblinoids could not stand against the might and madness of the alien invasion. By the time the Gatekeeper druids bound the Daelkyr and their servants in the depths of Khyber, the empire was a shadow of its former glory. Over the course of millennia it collapsed into savagery, and by the time humanity arrived on Khorvaire, all that was left of the empire was ruins and several clans trying to preserve the remains of the ancient lore and dreaming about the reestabilishment of the Empire.

Recently some of the Dhakaani clans have begun to vie for control of Darguun with another goblinoid clan that currently holds control of that territory, the Ghaal'dar clan, which have wrestled the territory of Darguun from Cyre during the Last War.

Most of the Dhakaani clans reside near the Seawall Mountains. They are divided into Kech Volaar and Kech_Shaarat clans.

The most recent significant event in the Eberron Campaign Setting is an event called the Last War, so-called because the people of Khorvaire believed that after the war was over everybody would grow tired of war (much as World War I was known as “the war to end all wars”). Coincidentally, the Last War ended on the 11th Day of Aryth (the equivalent to November 11, the day Germany signed the Armistice officially ending World War I). It refers to a series of conflicts in Khorvaire over 102 years that began with a dispute over the throne of the Kingdom of Galifar and the ruling of the Five Nations.

Two years prior to the end of the Last War, the nation of Cyre was destroyed in an incident known as the Day of Mourning. (The Eberron Campaign Setting does not give an official cause for this disaster, but it had a similar effect to the atomic bombings that ended World War II. Even a magical “radiation” mutates flora and fauna alike, similar to stereotypical but inaccurate depictions of the results of the nuclear radiation.) This event helped expedite the end of the Last War. Now, the region that was once Cyre is referred to as the Mournland and is the home of living spells, preserved dead bodies, and a militant sect of warforged (see Races) led by one called the Lord of Blades whose avowed goal is the total domination of the continent by the warforged at the expense of all “flesh and blood” humanoids. Those in the Mournland do not heal naturally, and magical healing has no effect. For all these reasons, few people enter the region.

The Last War officially ended two years prior to the start of the campaign, with the Treaty of Fort-du-Trône, as each of the Five Nations and most of the nations that broke off during the war officially became independent.

The Inspired are the psionically gifted rulers of Sarlona and willing hosts of their quori overlords. They are human-like in appearance, possessed of great physical beauty and were created over hundreds of years through the mixing of human stock with blood of demons and elves by the quori. As the ruling caste of the nations of Sarlona, the Inspired are loved and respected by the overwhelming majority of their subjects. To be selected as a host is a tremendous honor and the sole goal of virtually all Inspired.

Though they have recently acquired the ability to possess willing hosts of any type quori find the Inspired to be their preferred hosts; likewise an Inspired can never resist possession of the quori it was bred to host (in game terms Inspired are never allowed to make saving throws against possession attempts by their master). Over the decades that an Inspired is possessed, it develops a portion of the quori’s considerable psionic power (represented by gaining levels in psychic classes) even as its personality shifts to completely match that of its master.

While the recent trend in Dungeons & Dragons has been towards allowing players to play any race the Inspired are strongly discouraged as player characters, due to their utter domination by the near universally evil Quorien. Players who wish to play a psionic race or focus on the quori/kalashtar conflict are encouraged to play Kalashtar.