A familiar was a minor planar Spirit that had been summoned to service by, and magically bonded to, a Spellcaster. These familiars were little more than shapeless life forces prior to their summoning, but once bonded, became creatures of magical intelligence, gaining greater clarity and new powers. Typically, a familiar's form was limited to that of a Beast, but some spellcasters such as Warlocks had learned ways to summon familiars with magical properties, such as Imps or Pseudodragons. Invoking a similar power, Paladins could summon them as greater beasts, with even stronger familiar links.
Familiars and their masters shared an empathic link. For up to 1 mile (1.6 kilometers), a master could sense whatever emotions the familiar happened to be feeling. This mystical connection also meant that the spellcaster could have any spell granting a personal benefit affect the familiar as well, and magics linked to the caster's presence or memory could use the familiar's instead. Very powerful spellcasters, who had been bound to the same familiar for a long time, could eventually even scry through their familiar and use its senses.
When a familiar's was destroyed, their spirit would linger, and the spellcaster could re-summon their familiar in a new form by casting their spells again.