The Agile Manifesto is a set of guiding values and principles for software development that prioritize flexibility, collaboration, and responsiveness to change. It was created by a group of 17 software developers in 2001, who were seeking an alternative to traditional, heavyweight approaches to software development that they found to be slow, inefficient, and inflexible.

The Agile Manifesto consists of four values and twelve principles, which are:

Values:

• Individuals and interactions over processes and tools
• Working software over comprehensive documentation
• Customer collaboration over contract negotiation
• Responding to change over following a plan

Principles:

1. Our highest priority is to satisfy the customer through early and continuous delivery of valuable software.
2. Welcome changing requirements, even late in development. Agile processes harness change for the customer's competitive advantage.
3. Deliver working software frequently, with a preference for the shorter timescale.
4. Business people and developers must work together daily throughout the project.
5. Build projects around motivated individuals. Give them the environment and support they need, and trust them to get the job done.
6. The most efficient and effective method of conveying information to and within a development team is face-to-face conversation.
7. Working software is the primary measure of progress.
8. Agile processes promote sustainable development. The sponsors, developers, and users should be able to maintain a constant pace indefinitely.
9. Continuous attention to technical excellence and good design enhances agility.
10. Simplicity--the art of maximizing the amount of work not done--is essential.
11. The best architectures, requirements, and designs emerge from self-organizing teams.
12. At regular intervals, the team reflects on how to become more effective, then tunes and adjusts its behavior accordingly.

The Agile Manifesto emphasizes collaboration, adaptability, and continuous improvement, with a focus on delivering value to the customer. It has become a widely adopted framework for software development, and has influenced many other areas of business and project management as well.