How to merge two Outlook contacts folders?

Somewhere along the way my profile grew a second contacts folder and new contacts have been landing in both randomly for a year. Roughly 300 in one, 200 in the other, with overlap.

I want one folder and one address book. What is the procedure and how does the overlap get handled?

Pick the folder set as the default address book as the survivor, usually the one just named Contacts. Empty the other into it.

1

In the People view open the secondary folder, select everything with Ctrl+A and use Copy to Folder targeting the main Contacts folder. Copy first, so nothing is lost while you sort the overlap.

2

In the main folder switch to a list view: View, Change View, List, then sort by the File As column. Duplicate people now sit next to each other.

3

Walk the list and merge each pair by hand: open both entries side by side, complete the better one with anything unique from the other, delete the loser. With a few dozen overlaps this is a coffee break, not a project.

4

Delete the now redundant secondary folder, and check File, Options, Contacts to confirm the survivor is the default for the address book.

Worth thirty seconds of prevention: the second folder usually arrives with an added account or an import, and new contacts land wherever the current view points when you hit New Contact. Keeping the People view parked on the main folder stops the drift from restarting. If the overlap were in the hundreds rather than dozens, the CSV and Excel Remove Duplicates route covered in the multi PST merge thread linked in the sidebar scales better than hand merging.

Copied, sorted, merged about 40 pairs over coffee like you said. One folder, one address book, drift explained and stopped.