Two temples in Samarkand. Bibi-Khanym Mosque has no online ticket listed; Registan, Samarkand has 4 tickets and tours to book. The table and the two notes below put them side by side; the full pages have what to see, the ticket and the timing for each.
No online ticket is sold for Bibi-Khanym Mosque on its own. Entry works the simple way: you pay a modest fee at the gate on Tashkent Street, where foreign visitors are charged more than Uzbek citizens, and you can walk in whenever the site is open. A small extra charge is sometimes asked for photography or for a guide who waits at the entrance; settle the price before he starts talking.
Most visitors see the mosque as one stop on a walking tour of central Samarkand. The usual route starts at the Registan, follows the pedestrian street north-east for about ten minutes to Bibi-Khanym, crosses to the Siab Bazaar for dried fruit and bread, and continues uphill to the Shah-i-Zinda necropolis.
The Registan is an open public square framed by three madrasas, and you can see the facades from the edge of the square or the viewing area along the main road without paying anything. To walk onto the square and into the three courtyards and the gilded mosque you need a single ticket, sold at the booth by the entrance; it is valid for the whole ensemble, and there is usually an extra charge if you want to return for the evening illumination.
The tours sold online are built around timing and experience rather than access. Some run first thing in the morning, before the groups arrive, and finish with breakfast in a nearby teahouse.