An associate is a creature bound to the service of another. There are five types of associates in Neverwinter Nights — animal companion, dominated creature, familiar, henchman, and summoned creature — and a creature may have at most one of each type (except for henchmen, which may have a higher limit set by the module builder).
Associates are intended to aid their master, but whether they are always help or sometimes hindrance is subject to some debate. While they do try to help in battle, associates are known for sometimes choosing foolish ways to do so. (This can be ameliorated to some extent by installing an AI override from the Neverwinter Vault.) In addition, associates of a player character (PC) increase the size of a PC's party, which simultaneously causes more or tougher creatures to spawn from encounters and causes the PC to receive fewer experience points for killing a creature. (For a party with a single PC, this reduction is 20% for the first associate and reaches 50% at four associates.) These two considerations tend to cancel each other out, resulting in roughly the same experience per encounter, provided the associates were obtained before the creatures spawn. Summoning or dominating while in combat does cause a reduction in experience gained, assuming the battle could be won with different tactics. Overall, there is enough of a net loss of experience for some players to shun associates.