Kage

The title of Kage is reserved for the leaders of the five most powerful Hidden Villages. The five Kage are equal in power to the rulers of the counties in which their Villages exist. They oversee the daily operation of the Village, assign missions to Village Ninja, and are the over all leaders of the society of their village. The five Kage currently are:

Hokage 火影 means: Fire Shadow, Kage of Hidden Leaf Village (Konohagakure)
Mizukage 水影 means: Water Shadow, Kage of Hidden Mist Village (Kirigakure)
Tsuchikage 土影 means: Earth Shadow, Kage of Hidden Rock Village (Iwagakure)
Raikage 雷影 means: Lightning Shadow, Kage of Hidden Cloud Village (Kumogakure)
Kazekage 風影 means: Wind Shadow, Kage of Hidden Sand Village (Sunagakure)

At the time they are selected to be Kage, the candidate will usually be the most powerful Ninja associated with the Village. However, as time goes by and the Kage ages, younger Ninja hone and develop their skills. Eventually one of them may become more powerful than the Kage. No matter how powerful a younger Ninja may become, there can be only one acting Kage per Village at a time. The title of Kage is permanent once it's been installed on a Ninja. The title of Kage passes to a new Ninja if the current Kage dies or steps down. It is unknown if there are mechanics in place that would allow someone to challenge a sitting Kage for the position. The only history we know for sure is Konohagakure's, and its successions are all due to death or retirement.



S-Rank Ninja

S-rank ninja is not an official rank in the progression of a Ninja's career in the same way as Genin, Chunin, and Jonin are. Sometimes a ninja will develop skills and power far beyond the norm, even for those who've attained the rank of Jonin. S-rank Ninja have moved beyond being a ranked Ninja and have become legendary. Their official rank might be nothing if they've never gone through the testing, all the way up to being registered as a Jonin. Regardless of their recorded rank, they are incredibly talented Ninja.

An S-rank Ninja's ties to their village quite a bit. They may remain part of their village's forces like The Fourth Hokkage before he became Hokage or Kakashi's father Hatake Sakumo. They may remain loyal to their village and help when needed, but not be under any sort of formal control such as Jiraiya and Tsunade. They may also be villains or Nukenin such as Orochimaru or the members of Akatsuki and work towards their own personal goal. Regardless of their relationship to their villages, each village usually keeps track of S-rank Ninja in a book they provide to their members called the Bingo Book. The Village's Bingo Book keeps track of all notable Ninja, not just the ones from that village. Most Ninja will flee from an S-rank Ninja given the option, because even groups of Jonin wouldn't be able to defeat an S-rank ninja.

In addition to the slack they get with their relationship to their village, S-rank Ninja also often get cool, flashy nicknames. Some of Konoha's known S-ranks include the Densetsu no Sannin (Legendary Three Ninja) of Konoha: Jiraiya the "Gama Sennin" ("Toad Hermit") or "Ero Sennin" (PXXXXX Hermit), Orochimaru, and Tsunade "Densetsu no Kamo" ("Legendary Sucker" because of her poor skills in gambling) and "That Slug Woman". Another S-Class ninja of Konoha was the Fourth Hokage, called "Konoha no Kiiroi Senko" ("Konoha's Yellow Flash") before he became Hokage. Hatake Kakashi's father, Hatake Sakumo, was known as "Konoha no Shiroi Kiba" (Konoha's White Fang) before his disgrace.



Special Jonin

Tokubetsu Jonin are specialized ninja who fall in between Chunin and being a full Jonin. Instead of going through the training and testing to become a full Jonin, Tokujo instead focus on one particular field and become experts in it. So while a Tokujo may not be above Chunin level in Jutsu or Chakra control, they would be one the top experts in their particular field in their village.

In the Naruto storyline, pretty much everyone involved in the Chunin exam was a Tokujo. The examiners for the three stages - Morino Ibiki, Mitarashi Anko, Gekko Hayate, and his replacement Namiashi Raido were all Tokubetsu Jonin. The assistants, Shiranui Genma and Yamashiro Aoba, were Tokubetsu Jonin as well. The only one whos specialty has been revealed is Morino Ibiki: ANBU's interrogation expert and head of the ANBU Torture and Interrogation Force. Another Tokujo of note is Inuzuka Tsume, the mother of Kiba and Hana.

Jonin

Jonin are ninja with a lot of experience and exceptional personal skills and powers. In modern military terms, they'd be equivalent to an officer. Past the rank of Chunin what tests or qualifications Ninja need to move on in rank isn't really defined. As far as I know, there's been no mention at all of a Jonin exam or any other method testing Chunin to see if they're ready to be promoted. Ah well, maybe it'll be addressed as the storyline continues and the main characters who are Chunin start to move on up.

Anyway, Jonin are typically sent on A-rank missions or B-rank missions, and occasionally S-rank missions which are even more dangerous and rare than A-rank missions. They are also often assigned to lead three man teams of Genin to give the new Ninja the benefit of their knowledge and experience, as well as afford them an extra level of protection while they adjust to their new life as Ninja.

Unlike the promotion to Genin and Chunin, achieving the rank of Jonin doesn't seem to add another item like the forehead protector or tactical vest. I guess by the time you get enough experience to become a Jonin, you'd be getting bored with adding new uniform items.

Chunin

Chunin are ninja that have demonstrated they are capable of supervising or training other ninja. They'd be about the equivalent of a non-commissioned officer in the military. Some are put charge of a squad of Genin and become team leaders like Shikamaru, while others are instructors like Iruka, Naruto's teacher at the Academy. Some are even tasked to be secretaries and administrative assistants. Most Chunin however are just sent out to do C-rank missions or B-rank missions instead of performing the more specialized roles.

To become ranked as a Chunin, Genin must take part in the Chunin Exam, a grueling test that forces them to use all their skills as a ninja. Held twice a year, the Chunin exam consists of three parts, each one eliminating Genin without the skills to make it to the next stage. The first stage is a test of their ability to gather information secretly and their ability to make decisions. The second part tests their ability to adhere to guidelines while accomplishing a mission. The third and final stage is a series of fights between the candidates who passed the first two stages. Each fight is watched by a council who decide who is qualified to become a Chunin. Winning doesn't necessarily mean becoming a Chunin, and losing doesn't disqualify a candidate. The council seems to put more stock in a candidate's decisions and qualities they show while fighting than whether they win or not.

Originally, each Hidden Village held their own separate Chunin exam. After the 3rd Ninja World War the hidden Villages agreed to all hold their exams together at one village, and to rotate which village hosts the exam each time it's given. This was done to force the different villages to get to know each other and improve relations in order to help prevent another ninja world war. It also has the added benefit of putting all the different ninja in one spot so that prospective clients can see who they might like to hire.

Once a Genin is promoted to Chunin, they're allowed to wear a tactical vest with pockets for ninjutsu scrolls that resembles a modern flack vest. It's not clear if the vest is supposed to provide any actual extra protection or just serve as an indication of rank and give a Chunin a few more pockets to put stuff in. The vest doesn't appear to be a required item to wear though, as many Chunin and Juunin don't wear them at all and opt for other items to distinguish themselves.



Genin

Genin are the lowest rank of actual ninja in the Naruto Universe. Genin can be anything from an Academy Student who's just graduated all the way to a ninja who's been around a few years but hasn't been able to pass the Chunin (Middle Ninja) exam for whatever reason. As such, the abilities, power, and experience varies wildly amongst Genin. Even fresh out of the Academy, Genin represent a wide range of power level. Case in point is Sakura Haruno and Sasuke Uchiha. She's barely able to defend herself and he poses a credible threat to some Chunin.

Because of the varying levels of power and experience amongst Genin, they're put into four person teams when they graduate from the Academy. These teams typically consist of three Genin and one Junin to act as a mentor and squad leader. Each team is assembled based on the individual abilities of each Genin and are designed to balance out each other's deficiencies and "average" out the overall ability of each team. While in these teams, Genin get a chance to experience life as a ninja, hone their skills, and learn to work as part of a team, all while under the protection and supervision of one of their village's top ninja.

While Genin are ninja and work for their village, they're typically assigned to D rank missions, and on very rare occasions, some of the safer C ranked ones. D rank are typically risk-free, quick, and simple tasks such as finding a lost pet or manual labor, while a C rank mission might be escorting travelers.


Academy Stduent

While not technically a ninja rank, being an Academy Student is the first step to becoming a ninja. The Academy is where children go in the Naruto universe to learn the basic techniques of being a ninja. In classroom settings they learn Taijutsu and weapons such as the use of Kunai and Shuriken, Genjutsu (Illusion techniques), Ninjutsu, as well as chakra control.

Graduation requirements vary amongst each Hidden Village. In Naruto's Konoha, graduation is a combination of written exam and practical demonstration of basic techniques. However, in Hidden Mist used to use duels to the death until Momochi Zabuza killed his entire class. After that, they apparently changed to a non-lethal test.

Upon graduation the students become Genin (Low Ninja) and receive their hitai-ate, or forehead protector. The hitai-ate is a band of fabric with their Hidden Village's symbol etched into a metal plate. Despite being a forehead protector and means of declaring one's village, there's no uniform way of wearing the hitai-ate and just about everyone wears theirs in a different way, in some cases nowhere near their forehead.