Cross Referencing

JamieofGilead When you talk about cross referencing "huge" lists, I would recommend that you look into using PowerQuery. Connect to the lists in both files (NOTE: you don't have to load the files into Excel) and merge the two with a so-called anti-join.

Set it up correctly once and you can re-use the query over and over again, should the lists change in the future.

Now, you mention to be a novice. So, PowerQuery might seem a bit overwhelming. But this would be a good starting point, though:

https://exceloffthegrid.com/power-query-introduction/ , in particular chapter 15.

Alternatively, you would have to get into VLOOKUP, INDEX/MATCH type of functions (or XLOOKUP if your Excel version supports it) and filters to find the items on the "need list" that are not on the "have list".