The importance of third-party APIs in application integration lies in their ability to connect disparate systems, enabling data exchange and enhancing functionality. These APIs allow developers to leverage external services, such as payment processing, social media interactions, or data analytics, without needing to build these features from scratch. By facilitating interoperability, third-party APIs streamline development, reduce costs, and enhance user experiences. Moreover, they foster innovation by giving developers access to a wealth of resources and tools that can be integrated into their applications.