> For the complete documentation index, see [llms.txt](https://docs.infrastructure.finance/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.infrastructure.finance/usd.infra-vault/core-primitives-usd.infra-and-susd.infra.md).
# Core Primitives: USD.infra and sUSD.infra
**TLDR:**
* **USD.infra** is pegged to $1.
* **sUSD.infra** is a Vault participation token whose exchange rate reflects the Vault's net performance, subject to eligibility and transfer restrictions.
## **USD.infra: The stable unit**
USD.infra is a digital infrastructure-native stablecoin used as the settlement and accounting unit within the USD.infra Vault. USD.infra is non-yield-bearing. It is used for deposits, accounting, and movement of capital. USD.infra is issued on M0, a stablecoin infrastructure protocol, with backing that includes short-duration U.S. Treasuries.
## **sUSD.infra: The Vault participation token**
sUSD.infra is a Vault participation token representing a claim on the Vault's shared pool, subject to transfer restrictions and eligibility requirements.
## **Why two tokens**
The USD.infra Vault uses a two-token structure to separate the settlement asset from Vault participation, and to make Vault participation usable across supported DeFi venues, subject to applicable restrictions:
* USD.infra is the stable unit used for deposits, accounting, and movement of capital.
* sUSD.infra is the Vault participation receipt that makes Vault participation composable.
This structure allows for one yield token that can be used across many existing DeFi venues to lend, LP, loop, insure, bridge, and more, all while still accruing yield from financing real-world infrastructure.
Stable money in → Infrastructure financed → Cashflows back → Exchange rate reflects vault performance
