<p>Ok, the title tells everything.</p>
<p>Which ID number? Are you admitted already or did you only apply? Yale will send you your applicant number in the mail on a blue sheet of paper that says "DO NOT LOSE THIS PAPER". If you have already been admitted, they will send you your yale id later on after you matriculate.</p>
<p>I applied EA but didn't get an ID in the mail so I emailed
( <a href="mailto:online.decisions@yale.edu">online.decisions@yale.edu</a> ) and they emailed me all my info within a day or two. good luck!</p>