Asari are humanoids from the planet Thessia, with physical characteristics comparable to humans. They are one of the longest lived of the major Mass Effect races, with life expectancies of 1000 years or more. They often spend the first few centuries of their lives engaged in reckless pursuits, such as erotic dancing or mercenary work; this period is known as the Maiden stage. After a period of time, however, they usually feel an urge to settle somewhere and raise a family, entering the Matron stage of their lives. After a few centuries of raising children, they often move on into the Matriarch stage, becoming leaders and advisors to larger asari communities.
The asari are technically asexual, but their physical characteristics resemble human females, so they are referred to as females. Unlike most humanoids, they do not exchange genetic material when mating. The asari mating process involves a "merging" of the nervous systems of the mates, allowing the asari that chooses to conceive to "randomize" her own genes, using the mate's genetic code as an algorithm. Consequently, while asari are capable of mating with any humanoid, male or female, the offspring of the union is always asari. The greater genetic "randomization" that comes from mating with a non-asari has made interspecies matings preferred in asari society since their discovery of interstellar travel. Asari are capable of engaging in mating behavior without conceiving, and the process is typically pleasurable for both participants.
The control over their own bioelectricity that results from their mating process also gives asari a natural aptitude for manipulating element zero in their tissues; this trait, combined with the abundance of eezo in the environment of the asari homeworld, makes them natural biotics.
A small minority of asari develop a genetic condition that causes their partners to die when they mate; they are known as ardat-yakshi. The mating process is intoxicating for the ardat-yakshi, whose biotic powers grow stronger when she kills. Fortunately, ardat-yakshi are infertile, so the condition is not self-perpetuating. Also, ardat-yakshi are never produced when asari mate with non-asari (supporting the cultural preference for mating with aliens).
Asari do not naturally form large communities, and asari worlds are typically comprised of numerous city-states managed by councils of matriarchs. The Asari Republics are essentially a union of these city-states; a unified government is a relatively new phenomenon for the asari. All asari are able to participate in the government via the extranet, a situation that the asari call an "electronic democracy".
Just as they do not typically dwell in large, dense communities, asari do not typically organize large armies. Asari communities typically have numerous small commando teams for defense. Given the time they have to devote to training and their innate talent for biotics, asari commandos are exceptionally dangerous. That said, the asari depend on their turian allies for support in military conflicts that require large troop deployments.
Despite their low militarization in comparison with other factions in Mass Effect, the asari have 21 dreadnoughts in their fleet and lay claim to the single most powerful dreadnought owned by any Council race, the Destiny Ascension.