Genjutsu

Genjutsu (幻術; Literally meaning "Illusionary Techniques") is one of the three main types of techniques. Like ninjutsu, it is performed by using chakra and hand seals, but whilst ninjutsu creates physical effects, genjutsu works by creating illusions to deceive the target. This is done by manipulating the flow of chakra in the target's brain - specifically, their cerebral nervous system -, manipulating their senses to make them believe in what is not happening.

The most common types of genjutsu used are ones that make the target believe they are in pain, as it is an easy way to hinder an opponent in a fight. Genjutsu in general, however, is not as commonly used as the ninjutsu and taijutsu for many reasons. Genjutsu, whilst potentially crippling, can only affect the senses and not directly deal physical damage. As such, it is only useful against other shinobi. Learning to create more powerful genjutsu requires a person to spend large amounts of time learning about the field - something that very few outside of specialists bother with.

As genjutsu target only those it will affect, the user cannot always tell whether or not their techniques are successful, and the shinobi being attacked could break out of it and pretend not to have in order to surprise them. Finally, almost all genjutsu can be nullified by the technique Genjutsu Dissipation, which is a general skill that almost all shinobi know how to use. Once one genjutsu is discovered, the shinobi being attacked will be more wary of the user, especially since there is a good chance they might be a specialist. On top of all of that, genjutsu takes a lot of skill and intelligence to master. However, because genjutsu can target any of the five senses, an expert can defeat enemies without movement or even detection, which makes it a viable skill regardless. It is also very useful for mentally torturing a captured enemy, making it useful for interrogation and deception.

Combating Genjutsu
There are several ways for shinobi to combat genjutsu:
 * The general skill known as Genjutsu Dissipation is known by almost all shinobi, and can be used to dispel the illusion once it is cast. The technique requires hand seals to perform it, which means that is the illusion prevents movement, the technique cannot be used.
 * Shinobi with the Sharingan can see through and break genjutsu using it.
 * Intense pain can shock the senses back into order, dispelling any illusions being used on the person.
 * Ocular genjutsu can be avoided by using simply stopping the caster and the target from making eye contact.
 * A shinobi that is capable of sensing chakra will be able to tell when either theirs or another person's chakra flow has been disrupted and thus know when somebody is under a genjutsu.