I am trying to find which items in Column B are missing from A (finding the
reverse would be helpful to; any in column A not in column b)

Column A has data in 389 rows (A2:A389)
Column B has data in 400 rows (B2:B400)

I thought the formula below in Column C will call out the differences

=IF(B2=$A$2:$A$389,"Yes", "") then drag down to 400.

Ideas. Thanks.