The main use of application programming interfaces (APIs) is to facilitate interactions between different software applications. APIs define the methods and data formats that programs can use to communicate with each other, enabling developers to build applications that leverage functionalities of existing services or systems. This promotes modular development, where functionalities can be reused and integrated efficiently. APIs are crucial for enabling web services, mobile applications, and cloud computing solutions, allowing disparate systems to work together seamlessly. They enhance interoperability and make it easier for developers to access complex software functionalities without needing to understand their underlying implementations.