The Manifesto for Agile Software Development came out of a discussion among 17 people in the Utah mountains. The story around the start in the Snowbird ski resort is an interesting read, but fundamentally it is about looking for a better way of doing software development, and by extension, almost any other delivery activity.
Agile is a simple idea at its heart, though an entire industry has sprung up around the idea and approach, in many cases, making it anything but agile!
The Manifesto for Agile Software Development is as follows
We are uncovering better ways of developing
software by doing it and helping others do it.
Through this work we have come to value:
Individuals and interactions over processes and tools
Working software over comprehensive documentation
Customer collaboration over contract negotiation
Responding to change over following a plan
That is, while there is value in the items on the right, we value the items on the left more.