If you have someone's phone number and need to find his address, you have a couple of options. Several sites, including Yellow Pages, Intelius and AnyWho, offer "reverse phone directory" searches for finding out the name and address associated with a particular phone number. You can also pop the number into Google and see what the search engine spits back at you.

Visit the Yellow Pages reverse phone lookup website. Enter the full 10-digit number, including the area code, into the search bar. If the phone number is listed, a name and address should appear in the search results. Other sites including Intelius, AnyWho and AllAreaCodes.com offer a similar reverse phone directory search, which should reveal exactly whom a phone number is registered to. For unlisted numbers, these sites usually provide paid services that allow you to search deeper for the owner of a phone number.

Google makes it easy to look up a phone number. Just enter the phone number including the area code into Google's search field – for example, 123-456-7890 – and see what comes back. If the number is attached to a business, the business will usually show up on the first page of search results. Private listings might also show up if the owner has placed his number somewhere on the web, such as a social network or personal website.

Visit your local library and ask to use its "criss cross directory." This is a special type of phone directory that contains not only addresses arranged alphabetically by street with zip codes but also phone numbers in numerical order beginning with the prefix. Scan the list until you find the number you're looking for. The listing will show the name and address of the person belonging to it.

Take care with older phone numbers. Phone companies often change area codes when adding new ones, or they split areas off into separate code regions. If you're investigating an address via an old phone number, the area code might be different today. Use a phone number and area code locator to search the current area code, then run your reverse phone lookup with the new area prefix instead.