Have you ever seen a phone number on your caller ID or email address and wondering who it was? Well a reverse phone or email lookup would give you that answer. While using this kind of directory, your search will be reversed, meaning you will be looking for a name or address that goes with the phone number, instead of the opposite. Some services offer much more information than just an address. This can be useful if you are researching someone for a job interview or someone you have meet for example.

These kind of directories are often used by law enforcement and emergency services (such as 911 or police stations) to determine the location of a phone call. Because these include public and non-listed numbers, they are restricted to internal use.

Reverse phone lookup services first started in the Nineties, when telecommunication companies started offering the service for a small price. By the Noughties, this assistance had been made available for all online, raising some questions about the privacy of it.

To ease the customer's concerns, they were given the choice, for a small price, to take away their number from those directories, as long as they were landlines. Only land based phone lines can be included in this service; cell phone numbers still being out of any public 411 services.

More recently, forums and communities have formed on the internet, to help consumers identify various telemarketers, fundraisers and other companies who use this service to contact citizens. They can now trace, from using the phone number that showed up on their caller ID, what company has been calling them, most of the time over and over again.

The reverse phone lookup service can be really useful if you have the phone number but not the name that comes with it. All you need to use those directories is to find on the web the provider for your local area. This kind of service is now available online without costs and available for all to enjoy.