The significance of using APIs (Application Programming Interfaces) in modern software development lies in their ability to enable interaction between different software components and services. APIs facilitate seamless integration, allowing developers to leverage existing functionalities without needing to build applications from scratch. This promotes efficiency, as teams can focus on core features while enhancing applications with external data and services. Additionally, APIs drive innovation by allowing third-party developers to create complementary solutions. They also contribute to the scalability and flexibility of applications in an increasingly interconnected digital landscape.