Agile software development is a methodology that emphasizes flexibility, collaboration, and customer satisfaction. Here are the key concepts of Agile software development:

1. Individuals and Interactions over Processes and Tools:
   • Agile values people and how they communicate and collaborate more than the specific processes or tools they use.
2. Working Software over Comprehensive Documentation:
   • The primary measure of progress is working software. Documentation is important but should not hinder the actual development of functional software.
3. Customer Collaboration over Contract Negotiation:
   • Agile encourages continuous collaboration with customers to understand their needs and make adjustments throughout the development process.
4. Responding to Change over Following a Plan:
   • Agile is designed to be adaptable. It embraces change, even late in the development process, to better meet the customer’s needs.
5. Iterative Development:
   • Projects are broken down into small, manageable units called iterations or sprints, typically lasting 1-4 weeks. Each iteration results in a potentially shippable product increment.
6. Incremental Delivery:
   • Instead of delivering the entire project at once, Agile delivers small, incremental releases of the product to the customer, providing value early and often.
7. Collaboration and Communication:
   • Daily stand-up meetings (scrums) and regular reviews and retrospectives encourage frequent communication among team members and stakeholders.
8. Self-organizing Teams:
   • Agile teams are self-organizing and cross-functional, meaning they have all the necessary skills within the team to complete the project.
9. Customer Feedback:
   • Continuous feedback from customers and stakeholders is sought and used to improve the product.
10. Simplicity:
    • Agile promotes simplicity, focusing on the simplest solutions that will work, to reduce complexity and waste.
11. Sustainable Development:
    • Agile promotes sustainable development, with teams maintaining a constant pace indefinitely.
12. Technical Excellence and Good Design:
    • Continuous attention to technical excellence and good design enhances agility and the ability to adapt to changes.

These concepts are encapsulated in the Agile Manifesto and are supported by various Agile frameworks and practices, such as Scrum, Kanban, Lean, and Extreme Programming (XP).