polarizng and neutral density filter together

Quick, easy question (But I forgot the answer): Should polarizing filter be placed forward or behind a neutral density filter?

Thanks

Optically it should not matter.

Ease of handling would put ND on lens, CPL on ND, as the rotating element then only rotates the polarizer without rotating ND.
Also, depending upon brand of CPL, you might not have front threads on a CPL especially if it is a 'thin CPL'.

I have a thin ND and a thin CPL, and only the ND has front threads. The B+W CPL has no front threads.

With systems such a Nisi the polariser in the holder first and then the ND filter(s).

The Nisi Holder has facility to rotate the polariser independendantly of the holder and ND filters without need to remove the ND filters...

with regular NDs, I don't think it particularly matters. If you're using panel filters (LEE system, etc) and a high density ND, like the Big Stopper, it's best to put the ND in the slot closest to the lens in order to allow the foam gasket to do its job and minimize light leakage around the edges.

I would prefer to have vND on the lens first and rotate it to get right exposure first. And after it rotate polarizing one. From my real use of two, I've had polarizing first and then holder on top of it for slide-in welding grade ND. I quit very quickly from it.