What is Agile Development?

Agile methodologies emphasise people and their interactions, rather than processes and contracts. They emphasise flexibility over planning.

There is no single "agile methodology". Instead, the word "agile" is used to describe the characteristics shared by several methodologies that have arisen recently. These include Extreme Programming (XP) and less "extreme" alternatives such as Crystal Clear.

The core principles of agile development were documented 2001, in a document called the Agile Manifesto.

The key characteristics of agile methodologies are:

Deliver software frequently (delivery cycles vary from every couple of weeks to every couple of months)

Every release should work: i.e. the features it contains are fully tested and ready for use by the customer. Additional features are added in future releases.

The line between "design" and "development" is intentionally fuzzy. Each team member contributes to both.

Face to face communication is the dominant form of communication.

Business people and developers work closely together (meeting, informally, at least once a day in some agile methodologies).

Simplicity, "the art of maximising the amount of work not done", is an important design goal

The methodology expects, and supports, changes to requirements.

At first glance, agile methodologies may appear to be an excuse to cut corners, especially in the areas of formal design and documentation. For instance, design diagrams may be discarded once developers have finished with them, often by simply erasing them from the whiteboard where they were created! Developers may appear to start coding very early in the project, before all the requirements have been identified.

So, how can this possibly be a good thing? There are many answers, both theoretical and practical. I've outlined several of them here, and summarised other evidence supporting agility here.

Page History: Created Feb 04. Split into two parts, 22 Oct 04