Summoning Technique

is a space–time ninjutsu that allows the summoner to transport animals or people across long distances instantly via blood.

Contract
Before an animal summoning can be performed, a prospective summoner must first sign a contract with a given species. The contract comes in the form of a scroll, on which the contractor uses their own blood to sign their name and place their fingerprints and once signed it is valid even after the contractors death as long as the contract itself remains intact. After this they need only offer an additional donation of blood on the hand they signed the contract with, mould their chakra with hand seals and then plant the hand they signed the contract with at the location they wish to summon the creature. The amount of chakra used during the summoning determines how powerful the summoned creature can be.

It should be noted that anyone can summon a contracted animal as long as they have the blood from someone who has made a contract, the seal of the summoned creature, along with a source of sufficient chakra that the summon will accept. A creature is capable of determining who is attempting to summon it from the chakra used.

Improvement
While most summoners have only been shown capable of summoning one type of creature, Pain (through the Animal Path) has been seen summoning several different animals and even people. Pain does not provide a blood offering when performing a summon. Sasuke Uchiha has summoned snakes and hawks at different points, but unlike Pain he can apparently only summon one species at a time.

Other Information
Once summoned, the animal can perform a task or help the user in battle. The summon is not required to help the user, and may be more of a hindrance than an ally. In addition, summons are able to summon their summoner. They may also wear a forehead protector, suggesting a loyalty to only one village. Summoning can serve as a base for other techniques, as is the case with Summoning: Food Cart Destroyer Technique and Summoning: Quick Beheading Dance. It is also shown that summon animals can also choose when they can be summoned. In the event that they're busy with something, they can't be summoned, however they can have a substitute enter in their stead.

Trivia

 * In real-life Japan, the term refers to the practice of allowing spirits — like those of the dead or kami — to possess one's body and speak through it.
 * In the anime, it was shown that if a user attempts to summon an animal without first signing a contract, the user will be teleported to the home of the animal they have a natural affinity for.