_Follow along with the video_ --- > Welcome back! I'm Ciara, and I'll be guiding you through the Merkle Airdrop section of this course. In this project, we'll delve into **Merkle Trees** and **Signatures** to create our very own _ERC20 airdrop contract_. ### Airdrop An airdrop occurs when a token development team distributes tokens or allows people to claim them. These tokens can be of various types, including ERC-20, ERC-1155, or ERC-721. ::image{src='/foundry-merkle-airdrop/01-introduction/airdrop.png' style='width: 75%; height: auto;'} Tokens are typically given for free, with eligibility criteria such as contributing to the project's GitHub repository or participating in the community. This process helps to _bootstrap the project_ by distributing tokens to a **list of eligible addresses**. ### Walkthrough Let's quickly walk through the [code base](https://github.com/Cyfrin/foundry-merkle-airdrop-cu). In the source directory, you'll find the [Bagel token](https://github.com/Cyfrin/foundry-merkle-airdrop-cu/blob/main/src/BagelToken.sol), a minimal ERC-20 token that we will distribute. The [`MerkleAirdrop`](https://github.com/Cyfrin/foundry-merkle-airdrop-cu/blob/main/src/MerkleAirdrop.sol) contract is the cornerstone of this project, and it uses **Merkle Proofs** to verify address eligibility. It includes a `claim` function that allows addresses to receive the airdrop without paying gas fees. Furthermore, it implements _signatures_ to ensure that only intended recipients can claim the tokens. We will generate **scripts** to create Merkle Trees, Proofs, and Root Hash, as well as deploy and interact with the contract. In this course, we will cover several topics besides Merkle Trees and Merkle Proofs, such as signatures, the ECDSA (Elliptical Curve Digital Signature) Algorithm, and transaction types. - After initializing a ZKsync local node with Docker, we'll deploy the `Bagel` token and `MerkleAirdrop` contracts on it - We'll then **sign a message** to allow someone else to call `claim` on your behalf so you can receive the token while not paying for gas fees - The initial supply of tokens is created and sent to the airdrop contract - Finally, we can claim tokens on behalf of the claiming address (so they do not have to pay gas) using a signature - The address will now hold a balance of the airdropped tokens Let's get started!