# OP\_Return

The data representing Runes is stored within the OP\_RETURN field of a Bitcoin transaction.

OP\_RETURN is an operation code (opcode) from Bitcoin’s scripting language that enables users to embed arbitrary data onto the blockchain. The official limit for data stored in an OP\_RETURN field is 80 bytes, providing a dedicated space for storing information related to Runes.

The [official Runes documentation](https://docs.ordinals.com/runes.html) provides detailed explanations and guidelines on the specific usage and formatting of OP\_RETURN outputs for representing Runes data. This documentation serves as a valuable resource for developers and users interested in understanding and implementing the Runes Protocol within the Bitcoin ecosystem.

By utilizing the OP\_RETURN field, the Runes Protocol can seamlessly integrate [fungible](https://en.wikipedia.org/wiki/Fungibility) token data into regular Bitcoin transactions, without modifying the core Bitcoin protocol or introducing external dependencies. 

This approach aligns with the ethos of Bitcoin's decentralized and open-source nature, allowing for innovative applications and use cases to be built on top of the existing infrastructure.