Spirit Pact refers to the scrolls available for purchase in Final Fantasy XI that allow Summoners access to elemental spirits. Spirits are similar to enemy elementals that can be summoned by Summoners. They have a few advantages over avatars, and some major disadvantages that make their use somewhat rare and circumstantial. Their major advantage is that they can be summoned quickly when compared to avatars, making them useful as an emergency situation, and they are necessary to use the ability Elemental Siphon. However, their Perpetuation Cost is higher than avatars, their stats are lower, and the spells they use are impossible to control.
They use spells of their element (e.g., Fire Spirit will use fire-based spells), and the level of their spells is dependent on the level of the Summoner. Furthermore, as other summons, their magic strength and their Perpetuation Cost is based on used equipment, Summoning magic skill, and Vana'diel time. If Astral Flow is used, they receive an increased Fast Cast effect.