Editing D20 System (section)

== Mechanics ==
[[Image:Dice (typical role playing game dice).jpg|thumb|right|200px|Dice used in the d20 system.]]
The d20 System is a derivative of the third edition ''Dungeons & Dragons'' game system. The three primary designers behind the d20 System were [[Jonathan Tweet]], [[Monte Cook]], and [[Skip Williams]]; many others contributed, most notably [[Richard Baker (game designer)|Richard Baker]] and Wizards of the Coast then-president [[Peter Adkison]]. Many give Tweet the bulk of the credit for the basic resolution mechanic, citing similarities to the system behind his game ''[[Ars Magica]]''. Tweet, however, stated "The other designers already had a core mechanic similar to the current one when I joined the design team".<ref>{{Cite web |title=Amazon.com Message |url=https://www.amazon.com/exec/obidos/tg/feature/-/99666/ |access-date=26 January 2018 |website=Amazon.com}}</ref>

To resolve an action in the d20 System, a player rolls a 20-sided die and adds modifiers based on the natural aptitude of the character (defined by six [[Attribute (role-playing games)|attributes]]: Strength, Dexterity, Constitution, Intelligence, Wisdom, and Charisma) and how skilled the character is in various fields (such as in combat), as well as other, situational modifiers.<ref>{{Cite web |title=The Basics |url=http://www.wizards.com/d20/files/v35/Basics.rtf |url-status=dead |archive-url=https://web.archive.org/web/20050314020906/http://www.wizards.com/d20/files/v35/Basics.rtf |archive-date=14 March 2005 |access-date=12 November 2012}}</ref> If the result is greater than or equal to a target number (called a Difficulty Class or DC) then the action succeeds. This is called the Core Mechanic. This system is consistently used for all action resolution in the d20 System. In prior games in the ''D&D'' family, the rules for different actions, such as the first-edition hit tables or the second-edition ''[[Advanced Dungeons & Dragons]]'' (''AD&D'') "[[THAC0]]" and [[saving throw]] mechanics, varied considerably in which dice were used and even whether high numbers or low numbers were preferable.

The d20 System is not presented as a universal system in any of its publications or free distributions, unlike game systems like ''[[GURPS]]''. Rather, the core system has been presented in a variety of formats that have been adapted by various publishers (both [[Wizards of the Coast]] and third-party) to specific settings and genres, much like the ''[[Basic Role-Playing]]'' system common to early games by veteran role-playing game publisher [[Chaosium]].

The rules for the d20 System are defined in the [[System Reference Document]] or SRD (two separate SRDs were released, one for ''D&D'' 3rd edition and one for edition 3.5), which may be copied freely or even sold.<ref name="srd_faq">{{Cite web |title=System Reference Document: Frequently Asked Questions |url=http://www.wizards.com/default.asp?x=d20/srdfaq/20040123c |archive-url=https://web.archive.org/web/20040307092921/http://www.wizards.com/default.asp?x=d20/srdfaq/20040123c |url-status=dead |archive-date=March 7, 2004 |access-date=26 January 2018 |website=Wizards.com}}</ref> Designed for fantasy-genre games in (usually) a pseudo-medieval setting, the SRD is drawn from the following ''D&D'' books: ''[[Player's Handbook]]'' v3.5, ''[[Expanded Psionics Handbook]]'', ''[[Dungeon Master's Guide]]'' v3.5, ''[[Monster Manual]]'' v3.5, ''[[Deities and Demigods]]'' v3.0, ''[[Unearthed Arcana]]'', and ''[[Epic Level Handbook]]''.  Information from these books not in the SRD include detailed descriptions, flavor text, and material Wizards of the Coast considers more specific product identity (such as references to the [[Greyhawk]] [[campaign setting]] and information on [[Illithid|mind flayers]]).

[[d20 Modern]] has its own SRD, called the Modern System Reference Document (MSRD). The MSRD includes material from the ''[[d20 Modern|d20 Modern Roleplaying Game]]'', ''[[Urban Arcana|Urban Arcana Campaign Setting]]'', ''[[d20 Menace Manual]]'', and ''[[d20 Future]]''.  The MSRD can cover a wide variety of genres, but is intended for a modern-day, or in the case of the last of these, a futuristic setting.