Main is a lunar impact crater that is located near the north pole of the Moon.

The southern rim of this formation has merged with the larger crater Challis to the south, and the level interior floor connects the two craters through a narrower gap.

This formation consists of three overlapping craters that were joined together when the interior floor was resurfaced by lava flows, leaving a generally circular formation with outward bulges to the west and northeast.

The surviving rim of Main is a low slope that is nearly level with the surrounding terrain at its top.

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Main.