I'm sure there's a name for what I'm trying to do, but I don't know it so I
can't search previous questions for answers. Please help!

I have 2 lists:

List 1, column A - Customer names
List 1, column B - annual sales 2003

List 2, column C - Customer names (some of which are also on List 1)
List 2, column D - annual sales 2004

I want to match up customers that exist in both lists and be able to compare
2003 sales in a column right next to 2004 sales. The customers that don't
match up can be listed below.