Is this supposed to work, and if not, is there an alternative?

There's nothing wrong with the syntax of the first tag, but you're not telling us what you expect it to do, which would help in figuring out why it's "not" working. I've often found that when people use the boolean operators, they're using them backwards.

The second snippet, besides having a space after the colon that probably shouldn't be there, is testing if the entry's category has the literal name "Foo AND bar" which I doubt is what you're after.

Thanks.

This is what I want: If the current entry is filed under both categories of "foo" and "bar", then do something....