# Concepts
source: https://developer.mastercard.com/mastercard-gateway/documentation/concepts/index.md

## Recommended paths {#recommended-paths}

Select the path that matches your role and integration requirements.

|                                 If you are a...                                  |                                                 Then focus on...                                                 |
|----------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------|
| **Acquirer**, a bank or acquiring institution that enables merchants             | Understanding how gateway concepts support merchant onboarding, enablement, and compliance.                      |
| **Payment service provider**, a PSP, aggregator, or payment facilitator          | Understanding how to integrate with the gateway and support multiple merchants using shared concepts and models. |
| **Enterprise merchant**, a large merchant integrating directly with Gateway APIs | Understanding core gateway concepts and how they apply to direct integration and payment flows.                  |
| **Software vendor**, an ISV embedding payment flows into platforms               | Understanding how gateway concepts enable payment capabilities within software platforms.                        |

## API reference {#api-reference}

Use the API Reference to explore available endpoints, request and response models, and authentication requirements after understanding gateway concepts and personas.

For a complete list of supported APIs, see [API Reference](https://developer.mastercard.com/mastercard-gateway/documentation/api-reference/index.md).

## Versions {#versions}

These versions apply to concepts.

|             If you need...              |                                                                                                                                       Then...                                                                                                                                       |
|-----------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| **To integrate to an API**              | Use Version 100 of the Mastercard Gateway API for all new integrations.                                                                                                                                                                                                             |
| **Support for an existing integration** | Integration support starts from the minimum version documented in the API Reference. Refer to the [Versions](https://developer.mastercard.com/mastercard-gateway/documentation/api-reference/versioning/index.md) section for authoritative and up‑to‑date version support details. |

## FAQs {#faqs}

This section contains suggestions and solutions to the problems that may occur with your Concepts section.
Anyone integrating with the Mastercard Gateway APIs should start with this section, including acquirers, payment service providers, enterprise merchants, and software vendors evaluating integration options. No. Acquirers, payment service providers, enterprise merchants, and software vendors may integrate directly. Many merchants integrate indirectly through a payment service provider or a software platform. Implementation details and sample requests are available in the [API Reference](https://developer.mastercard.com/mastercard-gateway/documentation/api-reference/index.md).