### Rationale

The Asio library is intended for programmers using C++ for systems programming, where access to operating system functionality such as networking is often required. In particular, Asio attempts to address the following goals:

- Portability. The library should support, and provide consistent behaviour across, a range of commonly used operating systems.
- Scalability. The library should allow, and indeed encourage, the development of network applications that scale to hundreds or thousands of concurrent connections. The library implementation for each operating system should use the mechanism that best enables this scalability.
- Efficiency. The library should support techniques such as scatter-gather I/O, and allow protocol implementations that minimise data copying.
- Model Berkeley sockets. The Berkeley sockets API is widely implemented and understood, as well as being covered in much literature. Other programming languages often use a similar interface for networking APIs.
- Ease of use. Lower the entry barrier for new users by taking a toolkit, rather than framework, approach. That is, try to minimise the up-front investment in time to just learning a few basic rules and guidelines. After that, a library user should only need to understand the specific functions that are being used.
- Basis for further abstraction. The library should permit the development of other libraries that provide higher levels of abstraction. For example, implementations of commonly used protocols such as HTTP.

Although the current incarnation of Asio focuses primarily on networking, its concepts of asynchronous I/O can be extended to include other operating system resources such as files.