REST API integration is the process of connecting applications through their REST APIs, facilitating both internal operations and customer-facing functionalities. Common internal use cases include syncing data between CRM and ERP systems, while customer-facing integrations might involve connecting a product with HRIS for user provisioning. Best practices for REST API integration include thoroughly understanding API documentation, designing robust error-handling processes, and rigorously testing in staging environments before going live. Various tools are available for building these integrations, such as robotic process automation (RPA) software and integration platforms like iPaaS, with each suited to different scenarios depending on technical requirements and scalability needs. Merge, a leading unified API platform, offers a comprehensive solution by allowing access to hundreds of integrations across key software categories, enhancing both internal operations and customer experiences.