Dieter Shirley opened issue 721 in Ethereum's proposals repository at 18:31 UTC on September 22, 20171. His draft, dated September 20, 2017, carried an Axiom Zen email address. Axiom Zen was the Vancouver studio behind CryptoKitties, a game of digital cats, and Shirley was the game's technical architect5.
The draft named a new kind of token. An NFT is a token that stands for one specific item, such as one cat, so each unit differs from the next. Shirley stated the goal plainly: “A standard interface allows any NFTs on Ethereum to be handled by general-purpose applications. In particular, it will allow for NFTs to be tracked in standardized wallets and traded on exchanges.”1
His draft was rough by design. Under the functions, Shirley told readers to “expect this section to be significantly expanded after the first round of feedback”1. That thread drew 398 comments by GitHub's count.
Cats arrive before the standard
CryptoKitties went live on November 28, 2017, 67 days after the issue went up5. Growth came fast. By December 4, 2017, MIT Technology Review reported the game made up 12 percent of all transactions on Ethereum6. CoinDesk's December 4 report put it at 20 percent of all computations7. Users had spent at least $3 million on breeding, buying and selling cats, CoinDesk added.
Ethereum itself felt the load. The CryptoKitties team doubled its birthing fee, from 0.001 ETH to 0.002 ETH, citing congestion7. Nick Johnson, an Ethereum developer, gave CoinDesk the network's view. “CryptoKitties is definitely a significant contributor to network congestion, and it may have been what pushed us over the edge from mostly-full blocks to full blocks in the last day or so,” Johnson said.
Three stories ran on December 4, 2017: CoinDesk, MIT Technology Review and BrainStation's magazine. All three describe cats, breeding and network strain567. Each one skips the term ERC-721 and the draft behind the cats.
Shirley spoke for the game in one of them. “The CryptoKitties economy is entirely decentralized and impossible for the development team to manipulate,” he told BrainStation5. The final standard later cites the CryptoKitties contract as prior art for two controls2. One pauses all transfers, and the other blocks certain addresses from receiving NFTs.
Both sides, in their own words
Did a shared standard build that market?
“The deed is an NFT. If a piece of paper can represent your house, nothing else can represent it”
“What surprised me about the standards was that there’s no hash commitment for the data located at the URL”
The four authors who finished it
William Entriken took the draft to the finish. He opened pull request 841 on January 24, 2018, with the line "This pull request is the ERC-721 standardization document."3 It merged on March 9, 2018. On June 21, 2018, Entriken asked to move ERC-721 from Last Call to Final, and the change merged on June 224.
The final text lists four authors: Entriken, Shirley, Jacob Evans and Nastassia Sachs2. Its one-line summary reads: "A standard interface for non-fungible tokens, also known as deeds." The authors picked the word NFT after a survey, which found it "satisfactory to nearly everyone surveyed".
ERC-20 gets its due in the final text. Entriken and his co-authors say it “is inspired by the ERC-20 token standard and builds on two years of experience since EIP-20 was created.”2 In its section on backward compatibility, the final text gives CryptoKitties one line. The game is "Compatible with an earlier version of this standard," Entriken's team wrote.
Technical.ly profiled Entriken, who is based in Abington, near Philadelphia, in June 20218. He put the idea in house terms. “The deed is an NFT. If a piece of paper can represent your house, nothing else can represent it,” Entriken said.
How fast the market grew
NonFungible.com, an NFT data firm, sized the boom in its 2021 report10. Total NFT transactions rose from $82,492,916 in 2020 to $17,694,851,721 in 2021. That total counts sales plus minting, breeding and renting.
The number of people grew too. Active wallets rose from 89,061 in 2020 to 2,574,302 in 202110. Buyers went from 75,144 to 2,301,544. Sellers climbed from 31,774 to 1,197,796.
NFT buyers grew from 75,144 in 2020 to 2,301,544 in 2021, NonFungible.com counted
Wallets that held, bought or sold NFTs in 2020 and in 2021, by role
- 2020
- 2021
Source: NonFungible.com [10].
Read the chart as a table
| Item | 2020 | 2021 |
|---|---|---|
| Active wallets | 89,061 wallets | 2,574,302 wallets |
| Buyers | 75,144 wallets | 2,301,544 wallets |
| Sellers | 31,774 wallets | 1,197,796 wallets |
Where the trading sits in 2026
DefiLlama tracks a narrower set of marketplaces, with daily data from December 16, 202311. Its count shows a shrinking market that stays on Ethereum.
In the first quarter of 2024, its tracked NFT volume was $2,671.4 million11. Ethereum carried $1,576.2 million of that, or 59.0 percent. By the second quarter of 2026, the total was $68.0 million. The third quarter of 2026 came in at $113.8 million, and Ethereum carried $72.6 million.
Of the full quarters on record, Ethereum's share peaked at 81.6 percent in the fourth quarter of 202511. Polygon passed Ethereum once, in the third quarter of 2024, with $375.5 million to Ethereum's $344.9 million.
NFT trading volume fell from $2,671.4 million in Q1 2024 to $113.8 million in Q3 2026
NFT trading on the marketplaces DefiLlama tracks, by chain and quarter, in millions of US dollars
- Ethereum
- Solana
- Polygon
- Every other chain
- Height: Volume, $ millions
Source: DefiLlama [11].
Read the chart as a table
| Item | Ethereum | Solana | Polygon | Every other chain |
|---|---|---|---|---|
| Q1 2024 | $1,576.2M | $863.3M | $147.1M | $84.8M |
| Q2 2024 | $646.4M | $436.2M | $193.2M | $41.2M |
| Q3 2024 | $344.9M | $201.9M | $375.5M | $30.1M |
| Q4 2024 | $984.0M | $230.7M | $173.0M | $42.4M |
| Q1 2025 | $782.2M | $133.2M | $119.8M | $42.3M |
| Q2 2025 | $285.2M | $65.6M | $92.8M | $23.3M |
| Q3 2025 | $504.4M | $87.9M | $90.9M | $6.1M |
| Q4 2025 | $366.8M | $68.6M | $10.8M | $3.1M |
| Q1 2026 | $139.0M | $24.2M | $4.7M | $3.5M |
| Q2 2026 | $51.6M | $12.2M | $3.9M | $0.3M |
| Q3 2026 | $72.6M | $16.1M | $3.0M | $22.2M |
The case for the standard
Entriken argues the format reaches past art. “We need to be thinking about identity, healthcare and anything that needs to be authenticated in the real world,” he told Technical.ly in June 20218. He pointed to watches as proof. “If you buy a Breitling watch, you can’t buy one without getting an NFT,” Entriken said.
Numbers give his side a case too. One shared format lets wallets and markets handle any NFT the same way, as Shirley's draft promised1. NonFungible.com counted buyers rising 30-fold from 2020 to 202110.
The case against
Moxie Marlinspike, who calls himself a cryptographer, wrote up his test of the format on January 7, 20229. “What surprised me about the standards was that there’s no hash commitment for the data located at the URL,” he wrote. A hash commitment is a fingerprint of the image stored on chain, so anyone can check that a file matches.
Marlinspike built an NFT to prove the point. His test token showed one image on OpenSea and another on Rarible, and a poop emoji in a buyer's wallet9. “There’s nothing unusual about this NFT, it’s how the NFT specifications are built,” Marlinspike wrote.
The standard's authors made that choice on purpose. “The URI MAY be mutable (i.e. it changes from time to time),” Entriken and his co-authors wrote, using a house as their example2. Their house example and Marlinspike's emoji describe the same field9.
What to watch
Each side needs a different number. Entriken's case gains if NFTs spread from art to identity and health records, the uses he named8. DefiLlama's tracked volume, $113.8 million in the third quarter of 2026, is the figure to beat11.
Marlinspike's case gains each time a token's image changes after a sale. Ethereum, the standard's home chain, carried 63.8 percent of DefiLlama's tracked volume in the third quarter of 202611.
Sources
- Dieter Shirley (dete), "ERC: Non-fungible Token Standard (issue #721)," Ethereum EIPs (GitHub), Sept. 22, 2017, https://github.com/ethereum/EIPs/issues/721
- William Entriken, Dieter Shirley, Jacob Evans, Nastassia Sachs, "ERC-721: Non-Fungible Token Standard," Ethereum EIPs (eips.ethereum.org), created Jan. 24, 2018, https://eips.ethereum.org/EIPS/eip-721
- William Entriken (fulldecent), "EIP-721 Non-Fungible Token Standard (pull request #841)," Ethereum EIPs (GitHub), opened Jan. 24, 2018, merged Mar. 9, 2018, https://github.com/ethereum/EIPs/pull/841
- William Entriken (fulldecent), "721, the first graduate from the Last Call process (pull request #1170)," Ethereum EIPs (GitHub), opened June 21, 2018, merged June 22, 2018, https://github.com/ethereum/EIPs/pull/1170
- Max Greenwood, "Kittens and Crypto: Vancouver’s Axiom Zen is Behind a Viral Ethereum Video Game," BrainStation Magazine, Dec. 4, 2017, https://brainstation.io/magazine/kittens-and-crypto-vancouvers-axiom-zen-is-behind-a-viral-ethereum-video-game
- Mike Orcutt, "Ethereum’s First Killer App Is Here, and It’s a Game Where You Create Digital Cats," MIT Technology Review, Dec. 4, 2017, https://www.technologyreview.com/2017/12/04/147310/ethereums-first-killer-app-is-here-and-its-a-game-where-you-create-digital-cats/
- Alyssa Hertig, "Loveable Digital Kittens Are Clogging Ethereum's Blockchain," CoinDesk, Dec. 4, 2017, https://www.coindesk.com/markets/2017/12/04/loveable-digital-kittens-are-clogging-ethereums-blockchain
- Michael Butler, "This local technologist made Philly the birthplace of the leading NFT standard," Technical.ly, June 3, 2021, https://technical.ly/software-development/nft-william-entriken-standard/
- Moxie Marlinspike, "My first impressions of web3," moxie.org, Jan. 7, 2022, https://moxie.org/2022/01/07/web3-first-impressions.html
- NonFungible.com, "Yearly NFT Market Report 2021," read Oct. 13, 2026, https://nonfungible.com/news/analysis/yearly-nft-market-report-2021
- DefiLlama, "NFT marketplace volume by chain (overview, nft-volume)," read 03:58 UTC on Oct. 13, 2026, https://api.llama.fi/overview/nft-volume?excludeTotalDataChartBreakdown=false