# Populating Currency Selection Lists
source: https://developer.mastercard.com/enhanced-currency-conversion-calculator/documentation/use-cases/currency-selection-lists/index.md

## Context {#context}

An issuer building a cardholder-facing UI (for example, a currency conversion calculator or a transaction disclosure screen) needs to offer only the currencies that Mastercard and the ECB actually publish rates for, rather than a generic ISO currency list.

## Goal {#goal}

Retrieve the list of currencies Mastercard publishes a rate for, and the list of currencies the ECB publishes a euro reference rate for, to populate and validate currency selection lists.

## Actors {#actors}

* **Issuer User Interface** --- the cardholder-facing screen where a currency is selected.
* **Issuer Server** --- calls the Enhanced Currency Conversion Calculator API on the UI's behalf.
* **Mastercard Currencies Service** --- the `Mastercard-currencies` service.
* **ECB Currencies Service** --- the `Ecb-currencies` service.

## Preconditions {#preconditions}

* The issuer has a valid Mastercard Developers project with OAuth 1.0a credentials.

## Outcome {#outcome}

The issuer's UI displays currency selection lists limited to the currencies each rate source actually supports, reducing the chance of a cardholder selecting a currency pair that `GET /summary-rates` cannot resolve.

## How It Works {#how-it-works}

1. The issuer's server calls `GET /mc-currencies`, which takes no input parameters.
2. The Mastercard Currencies Service returns the count and list of Mastercard currencies (`alphaCd`, `currName`).
3. The issuer's server calls `GET /ecb-currencies`, which also takes no input parameters.
4. The ECB Currencies Service returns the count and list of ECB currencies (`alphaCd`, `currName`).
5. The issuer's server uses the Mastercard list to populate the transaction currency selector, and the ECB list to validate which currencies are eligible for the ECB reference-rate comparison used in [Cardholder FX Disclosure](https://developer.mastercard.com/enhanced-currency-conversion-calculator/documentation/use-cases/cardholder-fx-disclosure/index.md).

Diagram currency-selection-lists Tip: Both currency lists change infrequently. Consider caching them on your side and refreshing periodically, rather than calling them on every page load.

## Endpoint Reference {#endpoint-reference}


API Reference: `GET /mc-currencies`


API Reference: `GET /ecb-currencies`

## Next Steps {#next-steps}

|                                                            Category                                                            |                      Description                      |
|--------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------|
| [Testing](https://developer.mastercard.com/enhanced-currency-conversion-calculator/documentation/testing/index.md)             | Positive and negative test cases for these endpoints. |
| [API Reference](https://developer.mastercard.com/enhanced-currency-conversion-calculator/documentation/api-reference/index.md) | Try the Sandbox APIs directly from your browser.      |