Contacts in each category are viewed alphabetically. But you can decide whether you want to view them alphabetically by their first name, last name, or email address.

1. From your main Yahoo! Mail page, click the "Addresses" tab.
2. On the left side of your Address Book page, click the "Edit" link.
3. Click on the link Edit next to the name of the category that you want to change the layout
4. From there, use the pull-down menu to select the sort order. When you're done, be sure to click the "Save" button.