Collective Code Ownership

On an XP project, any programming pair who sees an opportunity to add value to any portion of the code can do so at any time. Everyone shares the responsibility for the quality of all the code.

Is Collective Ownership Essential?

Collective ownership is very valuable. It's probably possible to live without it; it's just not a very good idea. Collective ownership improves code quality, provides additional review of all the software without the need for explicit investment of time, and makes pair programming much more flexible and effective.