All the contributors to an XP project, developers, business analysts, testers, etc., work together in an open space, members of one team. The walls of the is space are littered with big visible charts and other evidences of their progress.
Planning is continous and progressive. Every two weeks, for the next two weeks, developers estimate the cost of the candidate features, and customers select those features to be implemented based upon cost and business value.
As part of selecting each desired feature, the customers define automated acceptance tests to show that the feature is working.
The team keeps the design exactly suited for the current functionality ...