Outlook: Finding Contacts Assigned in Both of Two Categories

How can I find contacts who are assigned to both of two categories?

You can use a filter for this. Choose View, Current View, Customize Current View, Filter. On the More Choices tab, in the Category box, type

cat1 AND cat2

where cat1 and cat2 are the categories you're trying to find. Click OK twice to apply the filter. The view shows only items assigned to both categories.