> For the complete documentation index, see [llms.txt](https://build.sovryn.com/builder-portal/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://build.sovryn.com/builder-portal/smart-contracts/fastbtc.md).

# FastBTC

This is the service that facilitates fast transfers from BTC to rBTC and vice versa.

FastBTC is the service that facilitates fast transfers from BTC (on the Bitcoin blockchain) to rBTC (on RSK), and vice versa. It consists of two separate systems

* BTC -> RSK FastBTC
* [RSK -> BTC FastBTC (bidirectional FastBTC)](/builder-portal/smart-contracts/fastbtc/rsk-to-btc.md)