Source compatibility enables a body of application source code to be compiled and operate correctly on multiple instances of an operating environment, across one or more hardware architectures, as long as the source code is compiled individually for each specific hardware architecture.

Source compatibility is defined by an Application Programming Interface (API), which is a set of programming interfaces and data structures provided to application developers. The programming syntax of APIs in the C programming language are defined in header files. These header files specify data types and programmatic functions. They are available to programmers for use in their applications, and are implemented by the operating system or libraries. The syntax of APIs are enforced at compile time, or when the application source code is compiled to produce executable binary objectcode.

APIs are classified as:

In all cases, application developers should seek to ensure that any behavior they depend on is described in formal API documentation, so as to avoid introducing dependencies on unspecified implementation specific semantics or even introducing dependencies on bugs in a particular implementation of an API. For example, new releases of the GNU C library are not guaranteed to be compatible with older releases if the old behavior violated a specification.

Red Hat Enterprise Linux by and large seeks to implement source compatibility with a variety of de jure industry standards developed for Unix operating environments. While Red Hat Enterprise Linux does not fully conform to all aspects of these standards, the standards documents do provide a defined set of interfaces, and many components of Red Hat Enterprise Linux track compliance with them (particularly glibc, the GNU C Library, and gcc, the GNU C/C++/Java/Fortran Compiler). There are and will be certain aspects of the standards which are not implemented as required on Linux.