From this information and these studies, later generations began comparing the different types of project management models, including waterfall, spiral and evolutionary delivery, to see if there was a way to improve upon these methods.From this arose the Agile Manifesto in 2001.

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It all started with 17 very influential agile development people.They defined what agile development was and what principles must be upheld in this model.The goals of agile software development were to put more value on individuals and their interactions, software that works, collaborating with customers, and quickly responding to any changes that may occur.
They also put together a set of principles that people should follow, which included ensuring customer satisfaction, emphasizing independent teams and delivering working software systems on a regular basis.
Later in 2005, an addendum was added to the Agile Manifesto, which put emphasis on checking for errors, reducing wasteful practices and helping workers empower themselves.
Please be sure to check out the other items in Bright Hub's collection of Agile project management guides and discussions.