Software engineers have traditionally considered any work after initial delivery as simply software maintenance. Some researchers have divided this work into various tasks, including making changes to functionality (perfective), changing the environment (adaptive), correcting errors (corrective), and making improvements to avoid future problems (preventive). However, many have considered maintenance basically uniform over time. Because software development has changed considerably since its early days, the authors believe this approach no longer suffices. They describe a new view of the software life cycle in which maintenance is actually a series of distinct stages, each with different activities, tools, and business consequences. While the industry still considers postdelivery work as simply software maintenance, the authors claim that the process actually falls into stages. They think both business and engineering can benefit from understanding these stages and their transitions.