The application designer and application programmer (or "application developer") design, build, test, and deliver mainframe applications for the company's end users and customers. Based on requirements gathered from business analysts and end users, the designer creates a design specification from which the programmer constructs an application. The process includes several iterations of code changes and compilation, application builds, and unit testing.

During the application development process, the designer and programmer must interact with other roles in the enterprise. For example, the programmer often works on a team of other programmers who are building code for related application program modules. When completed, each module is passed through a testing process that can include function, integration, and system-wide tests. Following the tests, the application programs must be acceptance tested by the user community to determine whether the code actually satisfies the original user requirement.

In addition to creating new application code, the programmer is responsible for maintaining and enhancing the company's existing mainframe applications. In fact, this is often the primary job for many of today's mainframe application programmers. While mainframe installations still create new programs with Common Business Oriented Language (COBOL) or PL/I, languages such as Java™ have become popular for building new applications on the mainframe, just as they have on distributed platforms.

Widespread development of mainframe programs written in high-level languages such as COBOL and PL/I continues at a brisk pace, despite rumors to the contrary. Many thousands of programs are in production on mainframe systems around the world, and these programs are critical to the day-to-day business of the corporations that use them. COBOL and other high-level language programmers are needed to maintain existing code and make updates and modifications to existing programs. Also, many corporations continue to build new application logic in COBOL and other traditional languages, and IBM® continues to enhance their high-level language compilers to include new functions and features that allow those languages to continue to take advantage of newer technologies and data formats.