How many books are there on attack titan?

There is only one manga series titled "Attack on Titan".

It's written and illustrated by Hajime Isayama, and it's been collected into 34 volumes.

It's important to note that there are also:

* Spin-offs: Like "Attack on Titan: Before the Fall", "Attack on Titan: No Regrets", etc.

* Artbooks: Containing sketches and behind-the-scenes information.

* Other related publications: Such as character guidebooks.

But the main story of Attack on Titan is contained within the 34 volumes of the main manga series.