> For the complete documentation index, see [llms.txt](https://www.digitalnations.xyz/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://www.digitalnations.xyz/web3-overview/the-web3-ecosystem/nfts/how-do-nfts-work/what-makes-a-token-non-fungible.md).

# What makes a token “Non-Fungible”?

The major difference between an NFT and traditional token is a concept known as “fungibility”.  While it sounds like a scary word – “non-fungible” is really a fancy way of saying “unique”.  For example: 

* **Fungible assets** are **not** unique, and you can easily swap them for another asset.  Currency (both traditional and crypto) is a great example of a fungible asset as you can always swap one dollar bill for another dollar bill or one Bitcoin for another Bitcoin 
* **Non-fungible assets**, on the other hand, are unique, and therefore cannot be directly swapped for other assets.  Most assets in life – art, real estate, shoes, couches, watches, etc… – are non-fungible (i.e., you can’t freely trade a shoe for a house) 
* **Semi-fungible assets**, like concert tickets, lie somewhere in between.  While any ticket could theoretically be swapped for any other ticket to the same concert, you couldn’t swap it for a ticket to *another* concert

                                  **Fungible vs. Non-Fungible. Vs. Semi-Fungible Tokens**

<figure><img src="/files/eFfjHJdOaKyd8CpAHYss" alt=""><figcaption><p>Source:  <a href="https://www.nature.com/articles/s41598-022-05920-6">Nature.com</a></p></figcaption></figure>

From a technical standpoint, fungible and non-fungible tokens are actually quite similar.  They both contain functions to check the supply and balance, transfer tokens and approve transactions.  The main difference is that non-fungible tokens each carry a unique ID, whereas fungible tokens do not (for Ethereum’s ERC-721 standard, this is known as a “uint256” ID)