> For the complete documentation index, see [llms.txt](https://docs.notional.finance/exponent/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.notional.finance/exponent/smart-contracts/system-overview.md).
# System Overview
User interactions on Notional Exponent are orchestrated by three primary types of contracts - lending routers, vaults, and withdraw request managers.
* **Lending routers** manage the interactions with the underlying lending protocols and the Notional Exponent vaults on behalf of users. Each lending protocol (like Morpho, Euler, or Silo) has its own dedicated lending router.
* **Vaults** manage share accounting on deposits and withdrawals and hold the yield tokens that generate yield for users. Vaults also hold the business logic that dictates how to convert between the deposit token and the yield token on deposits and withdrawals.
* **Withdraw request managers** handle the direct interactions with external protocols like Lido or Ethena to stake or redeem yield tokens like stETH or sUSDe. A yield token's withdraw request managers also handles the accounting for pending withdraw requests for that yield token.
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