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

# Core Concepts

- [Permissionless Pools](https://docs.spectra.finance/core-concepts/permissionless-pools.md): Liquidity providers are integral to any DeFi protocol, and Spectra is no different.
- [Principal & Yield Token](https://docs.spectra.finance/core-concepts/principal-and-yield-token.md): Principal Tokens (PTs) and Yield Tokens (YTs) are the core primitives and components of the Spectra protocol, also called as yield derivatives.