An important consideration in the deployment of each new release of system software such as Solaris is maintaining binary compatibility with applications built to run on earlier releases. If developers are not able to maintain binary compatibility with applications from one release of Solaris to the next, customers face a dilemma. Even though a new release may be extremely desirable from the standpoint of being faster, more functional, and of higher quality, the customer may not be able to upgrade for the simple reason that the larger the investment that has been made in applications the more likely that one or more of them may fail to work on the newest release. As a result, the customer may not be able to upgrade to this release until much later, when the offending application is itself upgraded. Recompilation is often not an option for simple economic reasons: even if the source code is available, the cost in time and resources to recompile, revalidate, and redistribute large numbers of applications to large numbers of systems is prohibitive.

Binary compatibility is based upon a system's Application Binary Interface, which is the set of supported run-time interfaces available for applications to use (as opposed to the API, which is the set of build-time interfaces). The most important part of a system's ABI is the set of interfaces provided by its shared libraries.

The Solaris ABI Program develops technology to define the Solaris ABI and evaluate applications' compliance with it.

Since the 4/01 release of Solaris 8, the core Solaris system libraries contain within them the definition of their ABI. This ABI is viewable with the pvs command. Symbols associated with the string "SUNWprivate" are private interfaces reserved for use by Solaris only; symbols associated with other strings (typically "SUNW_m.n") are supported public interfaces for application use and are intended to be stable, i.e., to not change incompatibly from release to release of Solaris. Applications using only such public interfaces should have no problems in running on any subsequent release of Solaris.

An application's usage of system interfaces can be checked either statically or dynamically. The former is easier, but is forced to simulate what will actually happen at runtime. The Solaris ABI program has developed two tools for checking an application's usage of Solaris interfaces: a static tool, appcert, and a dynamic one, apptrace.