Originally Posted by scucci
But what if I need multiple different groups access to a particular file or directory all with different permissions?
Do you mean users with different permissions, or a directory with different permissions?
If you have a number of different people, all of whom need access to a particular directory but that have nothing else in common:
1. Create a new group for this role.
2. Change the group ownership of the target directory to the new group.
3. For each user that needs access to the directory, make them members of the new group.