Summary

In this chapter, we have seen the ERC721 NFT standard, which is a bit different from the ERC20 token standard. Both the ERC20 and ERC721 standards serve different purposes and applications. ERC20 should be used when you need fungible tokens and each token has the same economic value. However, the ERC721 token should be used when you would need each token to be unique, and each of them can have different economic values. 

We have seen the ERC721 NFT standard implementation that the OpenZeppelin 2.1.1 library provides. As a developer, you must keep checking the OpenZeppelin library for any recent fixes or improvements to the ERC721 source code. There are many other libraries and contract files that OpenZeppelin provides, which we will have a deeper look into in the next chapter.