How do I copyright my website?

The US is a member of the Berne Convention which means users have the Copyright for their work and even have it without notice on the work itself (although I would recommend using it). (For a full list of countries who this also applies to see the list of other members.

You automatically have the copyright to any work you create. The United States Copyright Office is the official register of copyright. You can apply for trademarks and patents if you have anything that qualifies.

Put a copyright notice at the bottom and have proof you created the work but enforcement is kind of hard anyway. Even sites which copy you down to the slightest detail can escape it. There are rip-offs, down to the pixel, of stack overflow but they are in China and it's too hard to enforce. Don't fret too much about it.

If your really worried I would seek professional legal advice on how to protect your intellectual property which may well involve measures beyond copyright.

To register your website as legally copyrighted, assuming you are in the United States, you would visit the U.S. Copyright Office. From there, you could use their Electronic Copyright Office (eCO) to register your copyright. Their site also has a list of fees for performing this service.

Please note- you do not have to register your copyright to have your material copyrighted; it is legally copyrighted upon it's creation. Registering your copyright will add this as fact to the public record, and provides precedence in the event of theft of your work.

Once you have your site copyrighted, add a line somewhere in your site's design (usually found at the bottom of every page) which lists the year(s) in which the copyright was filed, and who the site is copyrighted to. Make sure you use the word "Copyright", or the copyright symbol (©, or © in HTML Entity form). "(C)" is not a legally recognized symbol for a copyright.

An example:

This comment is Copyright (©) Soleil Golden, 2010.

It is copyrighted automatically, but it is still good practice to put the copyright notice © - © not (c) at the bottom of your page.