The Agile Movement started in 2001 with a manifesto 
that was written by seventeen software developers.
>Agile software development is an approach to software development under which requirements and solutions evolve through the collaborative effort of self-organizing and cross-functional teams and their customer(s)/end user(s). It advocates adaptive planning, evolutionary development, empirical knowledge, and continual improvement, and it encourages rapid and flexible response to change.
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wikipedia
From this original gathering, some of the participants formed the Agile Alliance to promote agile practices in companies. Later, others formed the Scrum Alliance to promote Scrum agile practices. Additionally, local user groups of agile practitioners, such as PDXAgile , have been instrumental with promoting Agile practices in companies.