REST APIs and External Data Sources enable applications to connect with external systems and exchange data efficiently over the internet. REST APIs use standard HTTP methods such as GET, POST, PUT, and DELETE to send and receive information between applications and services. External data sources may include databases, cloud platforms, third-party services, or enterprise systems. These integrations help applications access real-time data and extend functionality without building everything internally. Developers use REST APIs to improve scalability, interoperability, and automation in modern applications. Secure communication protocols ensure reliable and protected data transfer. This approach is widely used in web, mobile, and enterprise application development.