My wife and I are battling across the gaming table about when attachment cards can be attached.

I could not find out in the rules. Nor did I find if they are to remain attached once committed to a character card.

The only time you can play attachment cards is during the marshall phase. The remain, unless due to effect, until the character is discarded or killed.

Thanks for the help. Now we can start having fun!

That's not actually true. Attachments normally get attached when they are played, but there are numerous attachments that can be played outside the marshalling phase - eg any attachment with the shadows crest or any attachment with ambush on it.

There are also attachments that have the word "Setup" in the text box. Those attachments can be played during setup.

There are also attachments that have the word "Setup" in the text box. Those attachments can be played during setup.

That's not actually true. Attachments normally get attached when they are played, but there are numerous attachments that can be played outside the marshalling phase - eg any attachment with the shadows crest or any attachment with ambush on it.

Technically, they are not "Played" -- that happens only during the Marshalling Phase. They are "Placed" (in Setup) or "Put into Play" (by Ambush or other Effect), or "Brought out of Shadows". It may sound nit-picky, but there is a distinct difference.