> For the complete documentation index, see [llms.txt](https://docs.usdd.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.usdd.io/introduction.md).

# INTRODUCTION

- [What is the new version of USDD?](https://docs.usdd.io/introduction/readme.md)
- [What is USDDOLD?](https://docs.usdd.io/introduction/what-is-usddold.md)
- [Why upgrade USDD?](https://docs.usdd.io/introduction/why-upgrade-usdd.md)
- [Core Features](https://docs.usdd.io/introduction/core-features.md)
- [Contract Addresses](https://docs.usdd.io/introduction/collateral-asset-contract-addresses.md)
- [Ecosystem Migration Progress](https://docs.usdd.io/introduction/ecosystem-migration-progress.md)