Many early attempts to improve software development focused on better ways of defining and detailing requirements, designing comprehensive architectures to support the requirements, and then developing the software in a very regimented, methodical manner to realize the system and supporting architecture.  Although some approaches were considered iterative in nature, they did not go far enough in addressing the needs of effectively managing rapidly changing requirements nor in accelerating the delivery of software. 

By the late 1990s, a majority of the software development processes that had been developed in the 1980s and 1990s were being criticized as bureaucratic, slow, and overly regimented.  In the mid-1990s, in reaction to these heavyweight software methods, there was a small contingent of industry thought-leaders promoting innovative approaches to software, enabling development organizations to quickly react and adapt to changing requirements and technologies. They realized that embracing change, and executing in a manner that not only accommodated this change, but fostered it, would result in a much more successful development strategy. 

The term "agile software development" emerged from a gathering of these industry thought-leaders in Snowbird, UT in 2001.  The term was first used in this manner and published in the now famous (or infamous) Agile Manifesto presented to the right.

This term was used as an umbrella reference to a family of emerging lightweight software development methods such as Scrum, Extreme Programming, DSDM, FDD, Crystal, and Adaptive Software Development.  Instead of emphasizing up-front planning and detailed requirements, these methods placed significant emphasis on continual planning, empowered teams, collaboration, emergent design, a test-early and often philosophy, and, most importantly, the frequent delivery of working software in short, rapid iterations.

Since the publication of the Agile Manifesto, other thought-leaders have continued to evolve agile thinking, drawing on lessons learned in other industries – for example, in the ideals and approaches promoted by Lean Development, and most recently, Kanban.