Find record from Table A that is not linked to Table B

I suspect this is fairly easy and possibly already has an answer in another thread, but I can't find one.

I have 2 tables (Table A and Table B) linked together through a third table (Link Table).  I am trying to find records from Table A that are not linked to Table B.  i.e. they don't exist in the Link Table.

How can I create a report that finds the records in Table A that aren't in my Link Table?  

Thanks.