parents'

"Parents' committee" is right.

PARENT'S is the possessive form of PARENT, so it means "of, or belonging to, a/the PARENT" (singular).
PARENTS' is the possessive form of PARENTS, so it means "of, or belonging to, the PARENTS" (plural).

Since a committee obviously has more than one person in it, the plural form is right.

Hello, Anonymous:

You have asked a really interesting question.

1. You are a learner. So it would be a good idea to follow the rule that KrisBlue explained.

2. If you read American newspapers, however, please do NOT be confused if you see:

a. Parents committee. (Some Americans in 2012 feel that apostrophes should be used only for

real possessi

James MSome Americans in 2012 feel that apostrophes should be used only for real possession.

Some Americans in 2012 feel that apostrophes shouldn't be used at all! :-)
(And it's not just Americans.)
Seriously though, I've not heard that rationale before; could you give a source or reference?

Great question, KrisBlue.

The best reference that I could find was The Associated Press Stylebook and Libel Manual (1994):

Do not add an apostrophe to a word ending in s when it is used primarily in a descriptive sense :

a teachers college
a writers guide

*****

I read the "travel" section of my newspaper (not that I wish to travel anyw

James MDo not add an apostrophe to a word ending in s when it is used primarily in a descriptive sense: a teachers college; a writers guide

I see. I personally don't like the rule, whatever rationale is behind it (and they don't state any), but that's a pretty formal source, so thanks for the info!

anonymous parents' committee or parent's committee which is the correct one