Extreme Programming organized software development around fast feedback from tests, integration, refactoring, customers, and short planning cycles rather than confidence in long upfront predictions.
Continuous Integration turned integration from a late project phase into a frequent automated feedback loop built around shared source, repeatable builds and automated tests.
The 2001 Agile Manifesto gave a shared name and set of values to several lightweight development movements that favored working software, collaboration and adaptation over rigid process.