Manga by Demographic

Shōnen 

Works whose intended viewing demographic is pre-teen and teenage boys. Probably the most universally appealing of the demographics. Experience the power of friendship, teamwork, and glowing martial arts.

Shoujo 

Works whose intended viewing demographic is pre-teen and teenage girls. These are the artists with the most detailed, dinner-plate-sized eyes and doki-doki butterflies.

Josei 

Works whose indended viewing demographic is young and adult women. Just as visually gorgeous as any shoujo, but with less diabetes..

Seinen

Works whose intended viewing demographic is young and adult men. In actually it contains just about every other demographic for some reason, and has a particularly odd fondness for moe aesthetics, even more so than the shoujo genre.