MoonMoon (no capitalization) can refer to the following:

* A term for a female with very large spherical breasts; it is an informal and slang term, usually disparaging.

* A lunar phenomenon involving the appearance of two moons in the night sky.

* MoonMoon_Ow (sometimes simply known as MoonMoon), an American Twitch streamer and YouTuber, popular for his streams of various video games.

* Moon-moon (sometimes stylized as "Moon Moon" or "MoonMoon"), an internet meme involving a poorly-behaved Shiba Inu dog.

* Moon Moon, a character from the comic series *Over the Garden Wall*.

* A common colloquialism in the Southern United States for a foolish or unintelligent person.