Filter data from one workbook so it doesn't appear in another

[vip3rpilot]

I have two large sets of data in two different sheets. Sheet A contains over 6000 sites, each with a unique site ID. In Sheet B are sites that meet certain criteria, and therefore will not be used for this particular project. The 3000+ sites in Sheet B also appear in Sheet A, but I wish to filter these out. Is there a way to specifically exclude site IDs in Sheet A that also appear in Sheet B?

[MarvinP]

Hi viperpilot (I speak leet).

I'd create a helper column on each sheet and do a CountIf(<ID Column on other sheet>, <ID on this sheet in this row>)

This formula would then be zero if it is unique or more than zero if it is a dup from the other sheet.