- A vampire group of shared "Blood" or heritage, who can trace their Generations back to a common ancestor, inparticular to the Third Generation. 
The clans are the major vampire lineages that comprise vampiric society.
Like all bloodlines, each clan has greater familiarity with a set of three Disciplines, a weakness largely unique to its members, and various stereotypes attributed to it as a result of a tendency to Embrace individuals with certain characteristics. The clans are generally differentiated and set above bloodlines by their greater number and influence throughout the world, identification with an Antediluvian progenitor, a history that reputedly extends back to the Second City, and clan weaknesses that were said to be handed down by Caine himself.
In the Final Nights, the thirteen clans are recognized. There is some ambiguity in the standards that determine clanhood. Two of the lineages, the Giovanni and Tremere, are actually recent replacements, having begun as bloodlines of established clans and risen to clan status within the last millennia after mostly wiping out Clan Cappadocian and Clan Salubri, respectively. Even though members of these fallen clans may yet survive, with their numbers so small and their Antediluvians destroyed they have been relegated to bloodline status, particularly as knowledge of their existence is gradually forgotten. On the other hand, several clans have held onto their positions despite the fact that their Antediluvians are believed to be dead. Likewise, the Ravnos are nearly extinct following the destruction of their progenitor during the Week of Nightmares, but they are still considered a clan (though some speculate that another bloodline will rise to take their place).
Very few non-vampires recognize the differences that set apart members of each clan and may in fact consider all vampires to be roughly the same as they all share a common ancestor (Caine). The majority of Cainites take the divisions and lineage in general quite seriously, particularly the Elders and those who know their complete lineage. During the Dark Ages, the High Clans and Low Clans marked the upper and bottom rungs of vampiric society, with one's ancestry greatly influencing the possibility for advancement and respect. Centuries later these class divisions would be abandoned for the division of sects between the Camarilla, Sabbat, and independent clans.
Each clan has its own organization and culture that is considered important by its members, and though individuals are rarely willing to make any self-sacrifice for their clanmates a general sense of understanding often elicits some preference for those of similar blood. Likewise, since vampires of any particular clan are often grouped together for political means, such as representation among the Primogen of a city, they may work together and present a unified front out of necessity. Such appearances almost always mask internal conflicts, however, and it is considered incredibly naive to treat all individuals of a clan the same.