The customer chooses what will deliver business value, chooses what to do first and what to defer, and defines the tests to show that the system does what it needs to.
Every software project needs to deliver business value. To be successful, the team needs to build the right things, in the right order, and to be sure that what they build actually works. Of course, this can't be done without programmers, but in fact the customer's role is critical in steering that process to success.
 In this book the pronouns "he" and "she" are used randomly to reflect the broad diversity that makes our industry great.
The customer role on an XP project can be filled by one person, or by several. The team will be most effective if the ...