Alder is a lunar impact crater that is located in the southern hemisphere on the far side of the Moon.

The inner wall of Alder is rough and slightly terraced, with the material scattered across the edges of the otherwise relatively flat interior floor.

Alder is associated with the only area in the basin not dominated by the pyroxene rocks typical of lunar lowlands.

This alder ejecta area is on spectrographic evidence instead principally anorthosite rock, typical of the lunar highlands.

[citation needed] By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Alder.