About the Evangelion Manga:
The Neon Genesis Evangelion manga is authored and illustrated by Yoshiyuki Sadamoto, the series character designer for Evangelion. The manga series began serialization in the Feruary 1995 issue of Shonen Ace, and is still being produced to this day.
Unlike the majority of anime series, Evangelion was not based on a pre-existing manga series. Both the Evangelion anime and manga are based off of an original concept written by Hideaki Anno and the other members of Project Eva at Gainax. Neither the anime nor the manga should be considered canon, as each stands on its own, storywise. On one hand, the manga began serialization months before the first episode was aired, but on the other hand, the anime finished very early on in the manga's production. For that reason, the two versions were initially very similar, but over time, the manga became quite different from the anime. The variation is a good thing at times, as the manga is supposedly more faithful to the original concept, and does not have to adhere to restricting formats like the series did. As such the manga places more emphasis on certain scenes and concepts that might not have recieved attention in the show. Also, the manga disregards some events from the anime series entirely. As an example, the episode with Jet Alone never occurs in the manga.
The entire manga series is slated to be 12 volumes in length, with 10 volumes completed. Stages contributing to volume 11 are currently being produced for Shonen Ace on a sporadic basis, and are fan translated upon publication by Bochan_Bird. To keep current, you can read the stage translations here at Eva Monkey, or by subscribing to the English Language Evangelion Mailing List.