 <p>In the first edition of "XP explained", there was twelve practices. </p> <p>In the second edition, the practices have been reorganized: some have been renamed or merged, some have been removed (Metaphor), and there now are: thirteen primary and eleven corollary practices.</p> <p>Under the "First Edition Practices" topic in the page you mentioned, one can find the original list of twelve practices and how they appear in the update.</p> <p>While reading, you'll certainly will people differentiating XP and XP2e (XP second edition).</p> <p>Likely, there was four principles in the first edition and a fifth one (Respect) was introduced with the second edition. </p>