> For the complete documentation index, see [llms.txt](/ja/llms.txt).

Interoperability covers how assets and messages move between Bitcoin, Rootstock, and other networks. Rootstock connects Bitcoin proof-of-work security to EVM-compatible smart contracts through bridges and messaging protocols.

## Core Pillars

| Pillar | Description | Best Use Case |
| :--- | :--- | :--- |
| **[Swap SDK](https://github.com/rsksmart/rsk-swap-sdk)** | Enable secure movement of assets between Bitcoin and Rootstock using the Swap SDK. | Trustless DeFi & L2 interoperability. |
| **[PowPeg](https://github.com/rsksmart/powpeg-sdk)** | SDK for creating native peg-in and peg-out transactions following the PowPeg protocol. | Institutional & high-value transfers. |
| **[Flyover SDK](https://github.com/rsksmart/flyover-sdk)** | A liquidity-based fast bridge that uses LPs to front the funds for the user. | Retail users & fast dApp onboarding. |
| **[Union (BitVMX)](https://github.com/rsksmart/union-bridge-contracts)** | A trust-minimized 1-of-N bridge that uses optimistic fraud proofs on Bitcoin. | Trustless DeFi & L2 interoperability. |
| **[Layerzero](/use-cases/interoperability/rootstock-layerzero/)** | Build Omnichain Fungible Token (OFTs) on Rootstock with Layerzero. | Trustless DeFi & L2 interoperability. |
| **[LI.FI](/use-cases/interoperability/integrate-lifi/)** | Omnichain liquidity routing from Ethereum, Arbitrum, Base, and more directly to Rootstock. | Single-transaction cross-chain liquidity. |
| **[Wormhole](/use-cases/interoperability/rootstock-wormhole-messaging/)** | Send arbitrary cross-chain messages to Rootstock using Verified Action Approvals (VAAs). | Cross-chain governance, data sync & multi-chain app logic. |

## Key Concepts

### 1. Peg-In (Bitcoin to Rootstock)
A Peg-In occurs when you send native BTC to a designated vault address on the Bitcoin network. Once confirmed, the Rootstock network mints an equivalent amount of rBTC to your Rootstock address.

### 2. Peg-Out (Rootstock to Bitcoin)
A Peg-Out is the reverse process: rBTC is burned on Rootstock, and the bridge infrastructure releases native BTC to your Bitcoin address.

### 3. Trust-Minimized Security (BitVMX)
With the advent of **[BitVMX](https://bitvmx.org/)**, Rootstock bridges are moving toward an optimistic verification model. This allows for Bitcoin-native fraud proofs, meaning that as long as one participant is honest, the bridge remains secure.

## Top Tools for Developers
* **[Flyover SDK](https://github.com/rsksmart/flyover-sdk):** The primary library for integrating near-instant bridging into your frontend.
* **[Swap SDK](https://github.com/rsksmart/rsk-swap-sdk):** Atlas Bridge is a cross-chain bridge for the Rootstock ecosystem. You can use it to move assets between Rootstock and other supported networks.
* **[LI.FI](/use-cases/interoperability/integrate-lifi/):** Leading cross-chain liquidity aggregator to route swaps and bridges into Rootstock.
* **[Rootstock Explorer](http://explorer.rootstock.io/):** Visually track cross-chain transactions and bridge health.

## Implementation Guides
Explore the recipes below to start integrating bridging solutions into your application.