While the RUP framework allows for the adoption of either a lightweight or a heavyweight approach, RUP tends toward a high-ceremony, heavyweight process due to the emphasis it places on project artifacts.
In recent years, the software development community has invested significant effort in establishing overtly lightweight processes that rely on a minimum level of ceremony to deliver quality software solutions for systems with emergent or rapidly evolving requirements. Efforts in this area by the leading methodologists have given rise to a number of new development processes, collectively known as agile methods.
Processes of this type are based on incremental development with timeboxed iterations. They differ from process frameworks such as RUP in that they emphasize the importance of performing a particular activity rather than producing a specific artifact. Such processes lay claim to being people-centric as opposed to document-centric.
The software engineer has a number of these methods from which to choose, including SCRUM, Crystal, and feature-driven development (FDD). However, by far the most well known of the agile methodologies is XP, and it is this process that we cover next.