Quality influences every decision we make... From hiring the best professionals to satisfying every client need. In order to deliver a quality product that meets or exceeds customer expectations, we rely on agile processes. We understand that requirements evolve and change during the project lifecycle and definitely during the product lifetime. These changes may be driven by new technologies like AJAX, which change user expectations. Changes become necessary when your organization grows - you will go from shared hosting to dedicated server to may be a load balanced server cluster (if your application becomes very popular). There is no such thing as future-proofed software. Source code must undergo continuous enhancements and refactorings. This is where agile methodologies come in. By creating automated unit tests, developers get the confidence to continuously refactor and improve. Changes to source code that break the application are caught by running automated tests.

A project is split into multiple time-boxed iterations. Depending on the nature of the project, each iteration would typically last 1 to 4 weeks. Each iteration would implement a set of use cases and feature sets. Customer interaction is crucial for the success of iterative projects. Customers must test and provide immediate feedback toward the end of each iteration.

Useful Resources
Introduction to Extreme Programming, J. Donovan Wells.
Wikipedia entry on Rational Unified Process.
Ward's Wiki for Wiki pages on refactoring.