> For the complete documentation index, see [llms.txt](https://futuresdoc.gitbook.io/perp-doc/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://futuresdoc.gitbook.io/perp-doc/english-1/parameters/underlying-currency-or-quote-currency-or-margin-currency.md).

# Underlying Currency | Quote Currency | Margin Currency

{% hint style="info" %}
Note: Compare and understand the differences between USDⓈ-margined futures contracts and coin-margined futures contracts.
{% endhint %}

## Three currencies form a contract

The most important parameters of the contract are the following three currencies, and various contracts are composed of these three currencies:

<table><thead><tr><th width="154"> </th><th width="103">Underlying Currency</th><th width="230">Quote Currency</th><th>Margin Currency</th></tr></thead><tbody><tr><td>USDⓈ-Margined Futures Contract</td><td>BTC</td><td>USDT、BUSD、USDC</td><td>Must be consistent with the quote currency</td></tr><tr><td>Coin-Margined Futures Contract</td><td>BTC</td><td>USD（always USD）</td><td>Must be consistent with the underlying currency</td></tr><tr><td>Hybrid Contract</td><td>BTC</td><td>USDT、BUSD、USDC</td><td>Any currency</td></tr></tbody></table>

### Underlying Currency / Quote Currency

The underlying currency/quote currency forms a currency pair, and the exchange rate of the currency pair is the price, which is the target of the contract transaction.

The most critical parameter of a contract is the 'underlying currency pair', which determines whether the transaction object is the price of BTC/USDT or the price of ETH/USDT.

### Margin Currency

After determining what to trade (the underlying currency pair), we need chips, which are the margin currency.

USDⓈ-margined futures contract is a contract that uses stablecoins as a bargaining chip. The margin currency must be consistent with the quote currency. If not, it is a hybrid contract.

A coin-margined features contract is a contract that uses the underlying currency as a bargaining chip, and the margin currency must be consistent with the underlying currency.

## Underlying currency pair | Index price

Whether it is a USDⓈ-margined or a coin-margined futures contract, the index price must be consistent with the underlying currency pair, because the meaning the index price is the market price of the underlying currency pair.

> Index price = underlying currency pair = underlying currency/quote currency

|                                | Underlying Currency Pair | Index Price |
| ------------------------------ | ------------------------ | ----------- |
| USDⓈ-Margined futures contract | BTC / USDT               | BTC / USDT  |
| Coin-Margined futures contract | BTC / USD                | BTC / USD   |