The tag wiki on this website says:

For questions about the d20 System, an RPG system originally published in 2000 by Wizards of the Coast. The d20 System was developed alongside D&D 3e and is a derivative of it, but it forms the mechanical backbone for a variety of RPGs entirely departed from the D&D system.

And the wiki page says:

The d20 System is a role-playing game system published in 2000 by Wizards of the Coast, originally developed for the third edition of Dungeons & Dragons.1 The system is named after the 20-sided dice which are central to the core mechanics of many actions in the game.

Much of the d20 System was released as the System Reference Document (SRD) under the Open Game License (OGL) as Open Game Content (OGC), which allows commercial and non-commercial publishers to release modifications or supplements to the system without paying for the use of the system's associated intellectual property, which is owned by Wizards of the Coast.

It looks, at least to me, to be more of a trademark/legal matter than just using a d20.

But in any case, which roleplaying systems are derived from the d20 System?

It looks like D&D 4E is not covered by it, or at least the associated OGL, but I appreciate they are not the same thing. Whereas stuff like Pathfinder and d20 Modern do seem to be derived from it.

  • \$\begingroup\$ Did you want a list of D20 systems? Like e.g. D20 modern? Or were you looking for something having to do with liscensing and e.g. KRyan's answer is in the vein of what you are looking for. \$\endgroup\$ Aug 13, 2020 at 14:55
  • \$\begingroup\$ @Pleasestopbeingevil I think the former, a list of d20 systems, but not just all systems that use a d20. I think the only way they can be grouped is by the OGL? I don't know how you separate the two. \$\endgroup\$ Aug 13, 2020 at 15:14

2 Answers 2


D&D 3.0 and 3.5, though these inspired later editions.

The article d20 System Definitions: Frequently Asked Questions, published by Wizards of the Coast in 2001, defines "d20 System" as follows:

Q: What is meant by the term "d20 System"?

A: The term refers to the game engine used in Wizards of the Coast's hobby gaming roleplaying game. It is the basis for Dungeons & Dragons, Star Wars, and other products currently released or in development. The "d20 System" trademark consists of the words "d20 System" and the "d20 System" logo. Additional information about the trademark can be viewed at: tess.uspto.gov, by searching for "d20 system".

Another article, The d20 System Concept: Frequently Asked Questions, provides a more detailed definition:

Q: Is the d20 System just another term for "Dungeons & Dragons"?

A: Yes and no.

The current version of Dungeons & Dragons is the basis for the d20 system. The market research done to determine what gamers wanted out of an RPG game was used to determine what kinds of rules, and what level of complexity, would go into the game.

That foundation was also used to produce the Star Wars roleplaying game, and it will be used to create a number of future products now in development at the company.

Over the long term, the two identities will separate. Dungeons & Dragons will mean the specific brand identity of that game, and d20 System will mean the common shared rules and systems used by many different games.

Given the date of 2001 for these articles, "Dungeons & Dragons" in this context referred specifically to D&D third edition. In other words, the "d20 System" referred specifically to the mechanical basis of D&D 3.0, which was later used for several other Wizards of the Coast RPGs. This includes their versions of Star Wars, Call of Cthulhu, d20 Modern, d20 Future, and d20 Past, and of course D&D 3.5.

It's also important to note that the term "d20 System" was a specific a trademark owned by Wizards of the Coast. This means that even if you were to write your own RPG based on the d20 System (such as the fan-made Naruto d20 and Pokémon d20 projects), you couldn't actually advertise it as such—unless you made an official d20 System licensing agreement with Wizards of the Coast. The d20 System license only applied to 3e-era products, as it was revoked when 4th edition was released.

D&D 4th and 5th edition draw clear design influence from D&D 3.5, but the term "d20 System" is generally not used to refer to those editions.

With the release of D&D 4th edition, Wizards of the Coast no longer offered the d20 System license, instead using the Game System License (GSL) which did not use the term "d20 System". Two factors confusing this answer are:

  • D&D 4th edition first-party rulebooks had a d20 System logo on the back, and continued to assert Wizards of the Coast's ownership of the trademark "d20 System" in their credits sections.
  • The book Dungeon Master 4th Edition for Dummies (2009), erroneously claims on page 27 that products released under the GSL bear the d20 System logo. In fact, they bear a new D&D compatibility logo. Only first-party 4th edition works bore the d20 System logo shown there. The GSL applied only to D&D 4th edition, and no other editions or games.

D&D 5th edition again draws mechanical inspiration from D&D 3.5, including use of the d20-based ability check system as its core mechanic, and so on, but it doesn't use the term "d20 System" to describe itself. It does not use the d20 System license or GSL, but rather allows products to be released using a version of the Open Gaming License (OGL), which was previously offered for D&D 3e as an alternative to the d20 System license (See Is there a OGL or GSL license for D&D 5e?).

Some players use the term "the d20 system" in a generic sense, referring to RPGs which use D&D 3e-like mechanics, a description which would include D&D 4e, D&D 5e, and Pathfinder. However, these are technically not part of the "d20 System", which is essentially a brand for WotC's D&D 3e-based RPG products from 2000 to 2007.

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    \$\begingroup\$ Actually, the GSL was only used with D&D 4e. D&D 5e returned to use of a revised version of the OGL, and there are both an official OGL licensed SRD and third-party OGL licensed content based on said SRD. 5e does not of course use the term d20 System, but that's got nothing to do with licensing, it's simply because 5e does not use the d20 System. \$\endgroup\$ Aug 14, 2020 at 1:45
  • \$\begingroup\$ @AustinHemmelgarn Ah, I didn't mean to imply that 5e still used the GSL. I've edited my answer to be more clear. \$\endgroup\$ Aug 14, 2020 at 12:44

You’re conflating several issues. There’s Dungeons & Dragons (in its various editions), the d20 System, the d20 System Trademark License (with associated d20 System Trademark Guide), the Open Game License, and System Reference Documents. You didn’t raise any concerns about it, but the Game System License is also a part of this story.

The d20 System

The d20 System is a system of rules, originally based on D&D 3e and updated in parallel with D&D 3.5e. The rules of the d20 System were described in a System Reference Document (SRD), which at the time was simply known as the SRD (though that term has since also been used by other publishers, as well as by Wizards of the Coast for 5e, though the 5e SRD has nothing to do with the d20 System).

An aside: “a d20 system”

A concern about capitals was raised regarding “d20 System” vs. “d20 system.” As a name, “d20 System” is a proper noun and thus is capitalized (well, except for the “d,” but that’s a specific notation rather than typical English grammar). The phrase “d20 system” could, instead, refer to just any system that primarily uses a d20 for things, so you could describe a whole lot of systems that have absolutely nothing to do with the d20 System as “d20 systems”—but, perhaps due to the potential for confusion, I don’t see a lot of people doing that.

The Open Game License

The SRD, and thus the d20 System, were (and remain) intellectual property of Wizards of the Coast. In order for other publishers to use this content without infringing upon Wizards of the Coast’s copyright, they needed a license to use it. That license was the Open Game License (OGL), since Wizards of the Coast released the entire SRD (and thus the d20 System) under that license. This meant other publishers could agree to that license, and so long as they obeyed its requirements (including a copy of the OGL with their product, respecting “Product Identity,” and so on), they could use copyrighted material from the SRD in their own products.

No edition of D&D is based on the d20 System, but rather things are the other way around. Wizards of the Coast makes this explicit in their d20 System Trademark FAQ:

Q: What is meant by the term "d20 System"?

A: The term refers to the game engine used in Wizards of the Coast's hobby gaming roleplaying game. It is the basis for Dungeons & Dragons, Star Wars, and other products currently released or in development. The "d20 System" trademark consists of the words "d20 System" and the "d20 System" logo. Additional information about the trademark can be viewed at: www.uspto.gov, by searching for "d20 system".

Q: What parts of Dungeons & Dragons are Open Game Content?

A: None of the Dungeons & Dragons product line is Open Game Content. Currently the only Open Game Content released by Wizards of the Coast is the System Reference Document.

Q: What parts of d20 Modern are Open Game Content?

A: None of the d20 Modern product line is Open Game Content. Open Game Content from d20 Modern can be found in the Modern System Reference Document (ñMSRDî) [sic].

Q: What parts of Star Wars are Open Game Content?

A: None of the Star Wars roleplaying game is Open Game Content.

Q: What parts of Call of Cthulhu and Wheel of Time are Open Game Content?

A: No part of these games is Open Game Content.

Q: What about earlier editions of D&D?

A: No earlier editions of D&D are, or will be, released as Open Game Content.

Note that at the time this FAQ was published, D&D 3.5e was the latest version of D&D. None of this applies to D&D 4e or 5e, which aren’t related to the d20 System in any way.

However, while no edition of D&D is licensed under the OGL, other games are—most notably, perhaps, pretty much all of Pathfinder 1e’s mechanical parts are based on the d20 System, and are in turn themselves licensed under the OGL. Though Pathfinder 1e is based on the d20 System, it does not use the d20 System logo (see below), and so whether you want to call it a d20 System game or not is kind of a semantic argument. (Basically, since Pathfinder rewrites several facets of the d20 System, the argument is that it’s not a d20 System product because it isn’t compatible with d20 System—which is fair enough.) Pathfinder 2e no longer uses the d20 System, but it is still largely available under the OGL.

The d20 System Logo and the d20 System Trademark License

Products associated with the d20 System used the d20 System logo, reproduced here under Fair Use (educational, non-profit, etc.):

The d20 System logo, a “square graphic indicia with the words ‘d20 System’ that appears on the covers of all Wizards of the Coast d20-compatible roleplaying game products”

Wizards of the Coast not only has copyright to this image, but they also claim it as a trademark. That means (they claim) this logo is meant to indicate to consumers that a product is part of or compatible with the d20 System, and it may not be used for other purposes. So in order to include this mark on a product, one needed to license the logo. The standard license for doing so was the d20 System Logo Trademark License—the text of which no longer seems to be available (at least, the wizards.com links for it are dead). Many other publishers would license this logo so that they could market their products as being part of the d20 System.

This licensing scheme is precisely why I am explicitly calling out my usage of the logo as Fair Use—I have not agreed to that license (indeed, I cannot even find the text of the license in order to figure out what agreeing to it entails), so my use of the logo is unlicensed—in this case (I argue), a protected, allowed form of unlicensed use known as Fair Use (in the USA; most countries have analogous concepts but may have different names for it and they may vary in the details).

The Dungeons & Dragons logo (as used in 3e products)

The d20 System logo is distinct from the Dungeons & Dragons logo found on products published by Wizards of the Coast, and a few other products, during 3e. Again reproduced under Fair Use:

The D&D logo used for 3rd Edition and “v.3.5 Revised Edition” products, which consists of the words “Dungeons & Dragons” on three lines, with a sword lying horizontally, pointing to the right, depicted beneath the ampersand, all on a brown emblem textured to look like metal.

This is also Wizards of the Coast copyright and trademark, but there was no standardized license available for this logo. In order to use it, you had to work out a license with Wizards of the Coast privately. It is not known what the terms of these licenses were (they probably usually involved paying Wizards of the Coast a certain amount of money), but they were all specific to a particular product.

D&D 4e and the Game System License

No part of D&D 4e is available under the Open Game License. In lieu of OGL content, some 4e content was made available under the Game System License, which is very restrictive. Very little third-party work was performed under the GSL. Kenzer and Co. famously released their 4e content without licensing anything under the GSL—instead, they were just very careful about what they used with respect to copyright law, which they could do because their founder is a noted copyright expert. Wizards of the Coast never sued them for copyright infringement, so presumably they did it “right.” (In fact, in the past, it had been Kenzer who sued Wizards of the Coast for their infringement of his copyright, namely some comics in Dragon magazine that they re-published in a compilation volume without his permission. This is why 3e Kenzer products could use the Dungeons & Dragons logo instead of the d20 System logo—they won the right to do so as part of the settlement for this case.)

D&D 5e and the Open Game License again, but not d20 System

D&D 5e has published a new SRD, again available under the OGL, but only a very limited portion of 5e is featured in it. For many aspects of the game, only one example of a thing is available as open-game content—it mostly serves as enough of a foundation for third-party publishers to write their own examples following that baseline, rather than potentially serving as a resource for players to actually play the game (as the SRD did for 3e and 3.5e).

  • \$\begingroup\$ I probably am conflating things. I got the impression that d20 system and d20 System (note capitalisation) was important. Also, is pathfinder a consideration in this? \$\endgroup\$ Aug 13, 2020 at 14:48
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    \$\begingroup\$ @Pureferret As for “d20 System” and “d20 system,” “d20 System” is the name of a particular ruleset that’s used as the foundation of D&D 3e and 3.5e, as well as other games. Wizards of the Coast wrote it, and owns the copyright to it. They have licensed (most of?) that content under the OGL, so others can use it without infringing that copyright. But the licensing is the important part of that equation: without that, it would simply be WotC copyright that no one else could use. The OGL says others can, so long as they obey the license. \$\endgroup\$
    – KRyan
    Aug 13, 2020 at 14:53
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    \$\begingroup\$ As for “d20 system,” I suppose you could use that as a generic label for any system that uses a d20 heavily. For instance, one could label D&D 5e as “a d20 system,” since it uses the d20 primarily. I’m not sure I see a lot of people doing that, particularly since it’s easily confused with “d20 System,” but you could. \$\endgroup\$
    – KRyan
    Aug 13, 2020 at 14:54
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    \$\begingroup\$ @McKay Hm, ok, I thought because Fair Use is a positive defense, it still would be, but I’ve reworded—“unlicensed use” rather than “infringement” then. \$\endgroup\$
    – KRyan
    Aug 14, 2020 at 19:03
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    \$\begingroup\$ @Shane Eeeeeeh... Wizards of the Coast had a foundation for a game based on market research and analysis that was shared between those games, and then they also kind of polished that up and threw in some D&D stuff they were OK with sharing, and called that the d20 System. Ultimately, those things mostly came first. \$\endgroup\$
    – KRyan
    Aug 15, 2020 at 0:40

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