The manner in which Exaltation occurs varies, depending on the type of Exalt.
The Celestial Exalted - Solars, Lunars and Sidereals - undergo Exaltation when a Spark of Exaltation, originally created by their patron god - respectively the Unconquered Sun, Luna or one of the Five Maidens - joins with their P'o, or lower soul. Each Spark is a portion of the god's power, given independence and altered so that it may exist in harmony with a mortal soul. Solar and Lunar Exalted may receive their Spark at any time, though generally do so at turning points in their lives - during acts of great heroism, for example, or when near death. A mortal may only become a Solar or Lunar if the Loom of Fate has determined they are destined for greatness. Sidereal Exalted, who by their nature operate outside Fate, receive their Sparks at the moment they are born; this avoids complications in the Loom. Celestial Exaltations are overseen by Lytek, god of Exaltation, though the gods have varying influence over which mortals receive Exaltation.
Abyssal Exalted also receive a Spark, but the process is tainted; they receive Sparks stolen and corrupted by the Neverborn. At the moment before a potential Abyssal is to die, usually by violent means, a Deathlord communes with them, offering the chance to return from the brink as a Deathknight in the Deathlord's service. They must accept the offer to become Exalted, and are the only Exalted to have such a choice.
Infernal Exalted are created in various ways by the Yozis or their demon servants. Little is known about the exact methods, but supposedly the Spark (and soul) of an existing Exalt is swallowed and regurgitated by their new patron.
The Terrestrial Exalted (the Dragon-Blooded) do not receive a Spark. When the Elemental Dragons created them, they gave a portion of their power not to specific individuals, but to entire bloodlines. Exaltation among the Dragon-Blooded is therefore inherited, passed down in a manner similar to more mundane traits. The more powerful and better bred a Terrestrial is, the more likely his or her children will also be Exalted; Exaltation usually occurs during puberty.
Alchemical Exalted, like the Sidereals, begin their existence as Exalted, but that's where any similarity ends. A special diamond soulgem, containing the soul of a great Autochthonian hero, is inserted into the forehead of a body created from one of the five magical materials, granting it life as an Alchemical.