APIs, or Application Programming Interfaces, serve as bridges between different software applications, enabling them to communicate and share data. By providing a defined set of rules and protocols, APIs allow developers to integrate and extend the functionality of existing software without needing to understand its internal workings. This promotes seamless interoperability among different systems, enhancing the developer experience and accelerating the software development process. APIs also enable businesses to leverage third-party services, thereby fostering innovation and reducing the time and cost associated with application development.