An admit card (hall ticket or call letter) is your entry pass to the exam centre. The guides below explain, exam by exam, where the admit card is published, which login details you need, what to check on the printout and how to fix the most common problems before exam day.
Most bodies first release an exam city slip a few days earlier and the admit card closer to the exam. Release dates change every cycle, so we never guess them; the official site for each exam is listed on its page.