Tag for books with multiple time periods

I'd like a tag to use on books that have multiple time periods. You know the kind -- there's a "current" story line, and a "past" story line.

Anyone have any ideas?

Thanks

Not time travel, as there's no interaction?

No, not time travel. More like back-story, or flashbacks.

3 > There you are: flashback(s).

I use "achronistic" to mean out of direct time sequence. Generally a writing style I dislike, although a few authors can do it very well.

If I had any like that, I'd be inclined to tag "multiple timelines".

I use "intertwining timelines", mainly because authors using that technique will have the timelines echo each other or run along similar lines. I use it to parallel another tag of mine: "intertwining storylines", where the storylines occur at roughly the same time.