> ## Documentation Index
> Fetch the complete documentation index at: https://circle-devdocs-test-ai-codegen-component.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Modules

Modules are the building blocks of modular wallets. Built on smart contract
accounts (SCAs), they extend the business logic of Web3 applications. Each
module provides a solution component for a new use case. You can enable specific
modules in your app to meet specific business needs, such as automated
transactions, subscription billing, or event-triggered actions when integrated
with Circle Contracts. This makes USDC more programmable and enhances its role
as a medium of exchange.

<Note>
  **Note:** Modules are built on Circle's modular smart contract accounts (MSCA)
  technology and support the following standards:

  * ERC-4337: Enables account abstraction, allowing operations without an
    initial Ether balance, improving flexibility.
  * ERC-6900: Provides a framework for modular smart contracts that are
    customizable and extendable.
</Note>

You can also create custom modules to expand the ecosystem based on this
standard.

## Supported modules

The table below lists the modules that are available:

| Module Name      | Description                                                                                                                                                                                                                                                                                                                       | Module Address                                                                                                                                                                                          |
| ---------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Address Book** | Only allows you to transfer assets to a list of allowlisted addresses that is enforced onchain. Useful if you are building a vault for your treasury. <br /> <br /> • Add a list of address you allow sending ERC20, 721 or 1155 assets too <br /> • Any transfers of these assets outside that list of address will fail onchain | ✅ Available: <br /> MSCA version: **circle\_6900\_v1** <br /> Mainnet address: <br /> `0x0000000d81083B16EA76dfab46B0315B0eDBF3d0` <br /> Testnet address: `0x0000000d81083B16EA76dfab46B0315B0eDBF3d0` |