Character Class System

A type of Game System where a character's abilities are determined by the class that they choose. Most common in Role Playing Games, but recently it has begun appearing in other genres, particularly First Person Shooters. A character class is defined by the abilities that it lends to a character -- as such, two different characters of the same class are theoretically interchangeable, in that they can play the same role in the game because of their similar abilities. However, Character Class Systems have varying levels of Character Customization -- ranging from characters of a given class being literally identical to having so much variety that character class is no longer even a good indicator of that character's abilities. Character Class Systems frequently include one or more Point Build Systems as part of their rules to increase customizability.

One of the major differences between Character Class Systems (besides the classes that they offer) is how they handle "multiclassing". Because classes determine a character's abilities, giving a character multiple classes is a good way to expand their abilities, but the extent to which this is possible differs greatly. Sometimes classes are completely mutually exclusive, and a character is stuck with whatever class they have until they die. Sometimes they can "upgrade" their class at a certain point, either plot-based or level-based -- this upgrade may be linear (eg, a Squire becomes a Knight) or may allow for a branching path to different Prestige Classes (eg, a Knight can upgrade to The Paladin or a Black Knight, but not both). Some systems are more lenient about multiclassing, allowing characters to change classes whenever they want; however, these systems build in drawbacks as well. Usually, either you can only be one class at a time (eg, if you change classes from Knight to Mage, you lose all Knight abilities and gain all Mage abilities), or you can only advance one class at a time (eg, if you're a Knight/Mage, you have to choose whether to increase your combat skills as a Knight or your casting skills as a Mage; you can't do both at once). Both approaches have the advantage of increased versatility (a larger number of abilities) at the price of decreased potency (each individual ability is less powerful).

In RPGs, the most common type of Character Class System is the Class and Level System. See also Fighter, Mage, Thief for a common set of 3 types of classes seen in RPG class systems. However, many FPSes that feature classes don't have levels, relying instead on player skill. See Common Character Classes for a list of classes that frequently turn up in games with Character Class Systems. See Point Build System for the main alternative to a Character Class System.

First Person Shooters

 * Team Fortress 2, and its predecessor Team Fortress Classic, (and it's predecessor Team Fortress) are based entirely around classes. There are nine total, each balanced for different playstyles, situations, and enemies.
 * The Modern Warfare series uses classes for its multiplayer, though unlike the above, each class's weapons, equipment, and whatnot are entirely decided by the player.
 * Transformers War for Cybertron has Soldiers, Scouts, Scientists, and Leaders.

Tabletop Games

 * Dungeons and Dragons is the most famous, and the Trope Maker.
 * The third edition of D&D gave the world the d20 system, allowing other publishers to use the same general mechanics of the tabletop rpg Ur Example. Many - but not all - d20 rpgs also used classes.
 * Pathfinder, a spinoff of d20, is a Character Class System as well.
 * Both Old World of Darkness and New World of Darkness effectively use a Character Class System, with your clan, auspice, tradition, etc acting as your class.
 * Rifts has a system that can get a bit confusing at times. There's O.C.C.s (Occupational Character Class), as well as R.C.C.s (Racial Character Class) for non-human characters. Where it gets confusing is that sometimes a character's R.C.C. doubles as his O.C.C, and sometimes a player has to pick an O.C.C. as well as an R.C.C. Then there's P.C.C.s, for Psychic Character class, but that terminology is barely ever used in the books since functionally they're no different from O.C.C.s.
 * Earthdawn calls them Disciplines. They're somewhat more fleshed out than in many cases, with social context given, as well as how the worldviews of different disciplines work together (or don't). Also, if you act against your discipline (wizards not thinking things through if they have the time, beastmasters hurting animals that aren't attacking them), you may lose some of your powers.

JRPGs

 * Final Fantasy has used classes, usually called Jobs, from the very beginning. They run the gamut of "no class changes whatsoever" to "can change classes at will" to "can have all classes' abilities at once" to "doesn't actually uses classes".
 * A staple of Dragon Quest as well, at least after the first game (where there was only one character in your party).
 * Completely inverted in The Last Remnant; the main character can use every ability in the game, and a character's class is based off the abilities they use, rather than the other way around. Using only item arts, for example, will change Rush to a class that does extra damage with items. Different character classes have different bonuses, so it can be worth only using certain skills in order to obtain a desired class.

Western RPGs

 * Many games based on the Dungeons and Dragons Game System.
 * Baldurs Gate
 * Icewind Dale
 * Neverwinter Nights
 * Planescape Torment
 * Knights of the Old Republic, using the Star Wars d20 variant
 * Diablo
 * Dragon Age Origins
 * Mass Effect

Real Time Strategy

 * World in Conflict had four "Roles", albeit only in team multiplayer: Armor (tanks roughly equivalent to RPG Fighers), Support (mainly AA+repair = Clerics, but also artillery = Long-Range Wizards), Air (attack helicopters = damage dealing rogues), and Infantry (...bards?). Each player can only assume one of them and has to rely on the rest of their "party" to compensate their role's weaknesses.

Literature

 * The True Game features twelve different inborn magical "talents". These are mixed in myriad combinations to create literally hundreds of character classes like Herald, Bonewalker and King, used in the chess-like battles of the setting. People without a talent (normal humans) are called "pawns".

Web Comics

 * Homestuck has a system for SBURB players, which creates a mythological role for a character that forms the basis of their personal arc within a session and determines their powers. It combines a Class, such as Thief or Bard, with an aspect such as Light or Rage, leading to such combinations as Heir of Breath, Seer of Light, Knight of Time, and Witch of Space.
 * The Aspects and Classes also don't always correspond to the literal translation. Light, for example, denotes luck instead of literally light, and Bard is a destructive class.