Requirements engineering (RE) is the process of defining, documenting, and maintaining requirements in the engineering design process. It is a common role in systems engineering and software engineering.

The first use of the term requirements engineering was probably in 1964 in the conference paper "Maintenance, Maintainability, and System Requirements Engineering", but it did not come into general use until the late 1990s with the publication of an IEEE Computer Society tutorial in March 1997 and the establishment of a conference series on requirements engineering that has evolved into the International Requirements Engineering Conference.

In the waterfall model, requirements engineering is presented as the first phase of the development process. Later development methods, including the Rational Unified Process (RUP) for software, assume that requirements engineering continues through a system's lifetime.

Requirements management, which is a sub-function of Systems Engineering practices, is also indexed in the International Council on Systems Engineering (INCOSE) manuals.