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Introduction to ERC721 Tokens

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In the world of blockchain technology, Ethereum Tokens have revolutionized the concept of digital assets. One particular type of token that has gained significant popularity is ERC721, also known as non-fungible tokens (NFTs). With the ability to represent unique and indivisible assets on the blockchain, ERC721 tokens have found a multitude of applications, from digital collectibles to in-game assets.

In this tutorial offered by EatTheBlocks, you will be guided through the intricacies of ERC721 tokens. The video delves into various aspects, including an exploration of the key differences between ERC20 and ERC721 tokens, the identification of tokens in ERC721 through tokenId, and the step-by-step process of transferring ERC721 NFT tokens. Additionally, you will learn how to effectively enumerate all tokens associated with a specific address in the ERC721 standard. If you are interested in expanding your knowledge of Ethereum tokens, be sure to check out the full series which covers ERC20, ERC777, ERC1155, and more.

Difference between ERC20 and ERC721

ERC20 and ERC721 are both token standards on the Ethereum blockchain, but they serve different purposes and exhibit several key differences.

ERC20 Tokens

ERC20 tokens are fungible tokens, which means each token is identical and interchangeable with another token of the same value. These tokens can represent any divisible asset, such as a currency or a share in a company.

ERC20 tokens are widely used for Initial Coin Offerings (ICOs) and as a means of exchange within decentralized applications (DApps). They are a popular choice for developers due to their ease of implementation and compatibility with existing exchanges and wallets. ERC20 tokens adhere to a set of standardized functions defined in the ERC20 token standard, allowing for seamless integration with various platforms.

ERC721 Tokens

In contrast to ERC20 tokens, ERC721 tokens are non-fungible tokens (NFTs). Each ERC721 token is unique and cannot be exchanged on a one-to-one basis with another token of the same value. This uniqueness allows ERC721 tokens to represent non-divisible assets, such as collectibles, digital art, and in-game items.

ERC721 tokens adhere to the ERC721 token standard, which outlines the required functions for the management and transfer of these unique tokens. This standard includes functions for token metadata, ownership management, and transfer approval. Unlike ERC20 tokens, which are often used for financial purposes, ERC721 tokens primarily focus on representing ownership and creating scarcity within digital ecosystems.

How tokens are identified in ERC721

In ERC721, each token is assigned a unique identifier, known as a token ID. The token ID serves as the primary method of distinguishing between different ERC721 tokens within a smart contract.

The token ID is typically represented as a non-negative integer value. When a new ERC721 token is created, it is assigned a unique token ID, which cannot be duplicated across the entire blockchain. This uniqueness allows each token to have its own distinct characteristics, ownership history, and value.

Developers can choose how to assign and manage token IDs within their ERC721 contracts. They may opt to use sequential numbering, randomly generated IDs, or any other method that suits their specific requirements. It is crucial to ensure that the mechanism used for assigning token IDs maintains uniqueness and prevents any potential collisions.

Introduction to ERC721 Tokens

How to transfer ERC721 NFT tokens

Transferring ERC721 NFT tokens involves the execution of specific functions within the ERC721 smart contract. The core function responsible for initiating a transfer is usually called transferFrom. This function allows the current owner of an NFT token to transfer ownership to another address.

To initiate a transfer, you need to provide the token ID of the ERC721 token you wish to transfer, along with the sender’s address, the recipient’s address, and any additional parameters required by the contract. Once the transaction is confirmed on the blockchain, the ownership of the ERC721 token will be updated accordingly.

It is important to note that the transferFrom function only works if the sender is the current owner of the ERC721 token and has been granted the necessary approval from the current owner. This approval mechanism ensures that token owners have control over the transfer of their assets and prevents unauthorized transfers.

How to enumerate all tokens of an address in ERC721

Enumerating ERC721 tokens belonging to a specific address involves querying the ERC721 smart contract to retrieve a list of token IDs associated with that address. The ERC721 token standard provides the function tokensOfOwner as a standardized way to retrieve this information.

To enumerate all tokens of an address, you need to call the tokensOfOwner function and provide the address for which you want to retrieve the token IDs. The smart contract will return an array of token IDs owned by the specified address. By iterating through this array, you can access information about each ERC721 token owned by the address.

It’s worth mentioning that the tokensOfOwner function may have additional parameters depending on the specific implementation of the ERC721 contract. These parameters can be used to further refine the search, filter tokens based on certain criteria, or retrieve additional metadata associated with each token.

Introduction to ERC721 Tokens

Introduction to ERC721 Tokens

ERC721 tokens are a type of non-fungible token (NFT) on the Ethereum blockchain. While conventional cryptocurrencies like Bitcoin and ERC20 tokens are fungible, meaning each unit is interchangeable, ERC721 tokens represent unique and distinct assets.

The ERC721 token standard was introduced to enable the creation and management of unique digital assets, such as collectibles, digital art, virtual real estate, and in-game items. Each ERC721 token has its own distinct characteristics, ownership, and value, making them highly sought after for digital asset ownership and provenance tracking.

The introduction of ERC721 tokens revolutionized the concept of ownership and scarcity in the digital world. With ERC721 tokens, users can truly own and transfer unique digital assets in a secure and transparent manner, thanks to the immutability and decentralized nature of the Ethereum blockchain.

The concept of non-fungible assets

Non-fungible assets, as the name suggests, are assets that are not interchangeable on a one-to-one basis due to their unique properties. Unlike fungible assets, where one unit is equal to another, non-fungible assets have distinct characteristics that set them apart from one another.

Non-fungible assets can be both physical and digital. In the physical world, examples of non-fungible assets include artwork, real estate, and vintage collectibles. In the digital realm, non-fungible assets can take the form of digital art, game items, domain names, and even virtual real estate within virtual reality environments.

The advent of blockchain technology, and specifically the ERC721 standard, has enabled the representation and transfer of non-fungible assets in a secure, transparent, and globally accessible manner. Through the use of unique token IDs and smart contracts, non-fungible assets can be seamlessly managed and exchanged on the Ethereum blockchain.

Introduction to ERC721 Tokens

Unique items on the blockchain

Unique items on the blockchain refer to assets that are represented by non-fungible tokens (NFTs). These items possess distinct characteristics, ownership, and value, making them highly coveted within the blockchain ecosystem.

Unique items can take various forms, including digital art, virtual real estate, collectibles, and even virtual pets. What sets them apart from fungible assets like cryptocurrencies and ERC20 tokens is their non-fungibility. Each unique item is one-of-a-kind and cannot be exchanged on a one-to-one basis with another item of the same value.

The use of blockchain technology and standards like ERC721 has revolutionized the concept of ownership and provenance for unique items. With blockchain, the ownership history and attributes of these items can be securely recorded and verified, allowing for transparent and tamper-resistant digital asset management.

Cryptokitties as an example

Cryptokitties is a prime example of how ERC721 tokens can unleash the power of unique items and create a vibrant digital ecosystem. Launched in 2017, Cryptokitties is a blockchain-based game where players can collect, breed, and trade virtual cats represented by ERC721 tokens.

Each Cryptokitty is an NFT with its own distinct characteristics, traits, and value. Users can buy, sell, and breed their kittens, creating a dynamic marketplace for these digital feline companions. The ownership and transaction history of each Cryptokitty are transparently recorded on the Ethereum blockchain, ensuring the integrity and provenance of each unique cat.

Cryptokitties gained significant attention due to its innovative use of blockchain technology and its role in popularizing NFTs. It showcased the potential for unique digital assets and paved the way for the development of countless other NFT-based applications and games.

Introduction to ERC721 Tokens

Understanding ERC20 Tokens

ERC20 tokens are a type of digital asset token that follows a specific set of rules and standards on the Ethereum blockchain. They are fungible tokens, meaning each token is identical and interchangeable with another token of the same value.

ERC20 tokens were introduced to provide developers with a standardized framework for creating and managing tokens on the Ethereum platform. The ERC20 token standard defines a set of functions and events that developers must follow to ensure interoperability and ease of integration.

These tokens serve a variety of purposes, including utility tokens for accessing DApps, digital currencies, and ICO tokens. ERC20 tokens have gained significant traction due to their ease of implementation and compatibility with existing Ethereum infrastructure, such as wallets, exchanges, and smart contracts.

By adhering to the ERC20 standard, developers can leverage a wealth of existing tools, libraries, and protocols built around ERC20 tokens, making it easier to incorporate their tokens into the broader Ethereum ecosystem.


ERC20 and ERC721 tokens are both integral parts of the Ethereum blockchain, each serving distinct purposes. While ERC20 tokens are fungible and primarily used for financial applications, ERC721 tokens are non-fungible and cater to the representation of unique assets.

ERC721 tokens, with their ability to represent and transfer non-fungible assets, have unlocked new possibilities for digital ownership and provenance. They have given rise to innovative use cases such as virtual collectibles, digital art, and decentralized gaming ecosystems.

As the blockchain ecosystem continues to expand, new token standards may emerge, further pushing the boundaries of asset ownership and representation. With the continued development of standards like ERC721, the future of non-fungible assets on the blockchain seems promising, revolutionizing how we perceive and interact with digital items.

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