Between the 11th and the 13th of february 2001, seventeen software practitioners got together to discuss and define a common, lightweight approach to software development. The result? This historical manifesto, which probably ranks in importance together with the original NATO conference that coined and defined Software Engineering, Royce definition of the waterfall development method, structured program design, Hoare axiomatics, Fagin´s software inspections and Carnegie Mellon´s Software Engineeering Institute Capability Maturity Model (CMM).
"The Agile movement is not anti-methodology, in fact, many of us want to restore credibility to the word methodology. We want to restore a balance. We embrace modeling, but not in order to file some diagram in a dusty corporate repository. We embrace documentation, but not hundreds of pages of never-maintained and rarely-used tomes. We plan, but recognize the limits of planning in a turbulent environment."
Revisited this and read the history section for the first time-- what a gem to come from a ski trip at Snowbird.
In spite of all the flak it has been receiving lately, including Bertrand Meyer´s stylistic criticisms in "Agile!: The good, the hype and the ugly", this still remains a must-read for any budding or practising software engineer.
After you have read it, I would highly recommend you look into an agile process like Scrum, Lean or Kanban to see how the manifesto and its twelve principles translate into interesting practices.