From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Viz Media (formerly known as Viz, and usually stylized as VIZ) is headquartered in San Francisco, California, United States. It is an anime, manga, and Japanese entertainment company that was founded in 1986 as VIZ. In 2005, VIZ and ShoPro Entertainment merged to form the current VIZ Media, which is jointly owned by Japanese publishers Shogakukan, Shueisha, and Shogakukan Shueisha Productions.
VIZ translated and localized the Dragon Ball manga from start to finish. Starting from what would be Volume 17 of Dragon Ball, however, they began labeling the books Dragon Ball Z for the consideration of the anime viewers who may not have been familiar with the original Dragon Ball manga.
They have also published a number of other popular Japanese manga, such as Naruto and Bleach.
VIZ has released all of the volumes of Dragon Ball and Dragon Ball Z, however, they have edited and changed a few scenes to make it more child-friendly. For example, although they kept some nude pictures (such as Bulma in the shower and Son Goku nude in Volume 1), they put a bra over a nude Bulma in Volume 9. VIZ also edited out a gun that Artificial Human No. 17 was holding at a man.