Is there a list of changes that making ERC721 become non-fungible token and different from ERC20?

Are there examples of ERC721 contracts?

Is there any drawback of ERC721?

up vote 7 down vote accepted

We are still writing the ERC-721 standard. 721 is about deeds. 20 is about tokens. Here is some draft language in the specification that explains the difference


"Deed" word choice

The noun deed is defined in the Oxford Dictionary as:

A legal document that is signed and delivered, especially one regarding the ownership of property or legal rights.

This definition is consistent with the fact that ERC-721 contracts track ownership of other things, such as houses, pictures of kittens or collectable cards. If you gain ownership of a house via ERC-721 then the thing that the ERC-721 contract tracks is the deed, the place where you live is the asset.

Alternatives considered: non-fungible token, title, token, asset, equity, ticket


Regarding "deed" name

@Beskhue, backwards compatibility with existing contracts is not a design goal of this specification. Such is the risk of implementing standards that are not finalized. Please note that ERC-20 was designed as a consensus standard to meet existing implementations, and it suffered accordingly.

I argue that deeds are more general than tokens (and, by extension, NFTs). The word title is probably more correct, but title has other unrelated meanings that are much better known.

CASE STUDY, CRYPTO KITTIES: See the contract KittyOwnership code. In this case, the ownership contract concerns itself with who owns each kitten. This is distinct from the kitten itself. The kitten is defined in struct Kitty. (Warning: the links in this case study are an older version of CK, but they are representative of the actual deployed code.)

CASE STUDY, HOUSES: In most (all?) counties in the United Status, house ownership is recorded by a county deed recorder, the instrument of house ownership is a deed. The deed is distinct from the house. In fact, the house may change, the taxes on the house might change. However the deed is permanent, until it is transferred.

These two case studies illustrate how a deed is separate from the thing which it declares ownership over. In token standards, the token itself is what you have ownership over. In deed standards, you always want ownership of a separate thing. Such is the motivation for the distinct name.

Source: I'm the main author of https://github.com/ethereum/EIPs/pull/841

  • Thank you! That is helping me a lot. Now, I know what is "deed" comparing to token and erc721 is about deed, the ownership itself, not token. – Anderson Jan 31 at 5:38
  • I see the discussion thread but its quite long. May I ask what are the main issues why erc721 is not settled? – Anderson Jan 31 at 5:38
  • 1
    It was not settled because some people wanted more features in the standard and some wanted less, also naming things is a bitch. Also there was fragmentation because the original standard author left. Now we have achieved consensus and I do not expected any further changes to the standard. – William Entriken Mar 2 at 17:09
  • why cant we transfer them or see them in wallet like erc20 tokens? – Anam Nizami Mar 18 at 18:58
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    That question must be directed to each wallet vendor individually. Now is a great time to mention that I am speaking at explore721.com in Houston this weekend and wallet authors are VERY welcome to come, learn, and work with me so we can get this done! Please contact your wallet vendor to discuss this and invite them to contact me directly. – William Entriken Mar 19 at 19:11

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