Merging Contacts in Gmail Contacts List / Addressbook

If you have duplicate contacts, there are two ways you can fix this problem: merge your contacts manually, or have the system find and merge contacts automatically, as well as duplicate data within contacts.

To merge two or more contacts manually:

• Select the contacts you’d like to merge from your contacts list.
• Click the More actions drop-down menu, and select Merge contacts.
• Make any edits to the suggested solution (if you’d like to change anything).
• Click Save at the top of the page.
• To find and fix all of your duplicate data at once, use the following instructions:
• Open the Contact Manager.
• Click the More actions drop-down menu, select Find and merge duplicates.
• Gmail will display the names of the contacts with duplicate data. If an entry has only one contact, then the contact itself has duplicate data (repeated phone numbers, emails, etc.) If an entry has two or more contacts, be sure to check whether these are duplicate contacts; many people have similar names. You can expand them by clicking details next to each one and unchecking any that you don’t want to fix.
• When you’re ready, click Merge at the top of the list. [source]