htaccess is a very ancient configuration file that controls the Web Server running your website, and is one of the most powerful configuration files you will ever come across. To learn how to take htaccess to the next level, beyond what you thought possible, memorize this: Htaccess Guide
Common Htaccess error, more at
What Is .htaccess ^
Specifically, .htaccess is the default file name of a special configuration file that provides a number of directives (commands) for controlling and configuring the Apache Web Server, and also to control and configure modules that can be built into the Apache installation, or included at run-time like mod_rewrite (for htaccess rewrite), mod_alias (for htaccess redirects), and mod_ssl (for controlling SSL connections).
Htaccess allows for decentralized management of Web Server configurations which makes life very easy for web hosting companies and especially their savvy consumers. They set up and run "server farms" where many hundreds and thousands of web hosting customers are all put on the same Apache Server. This type of hosting is called "virtual hosting" and without .htaccess files would mean that every customer must use the same exact settings as everyone else on their segment. So that is why any half-decent web host allows/enables (DreamHost, Powweb, MediaTemple, GoDaddy) .htaccess files, though few people are aware of it. Let's just say that if I was a customer on your server-farm, and .htaccess files were enabled, my websites would be a LOT faster than yours, as these configuration files allow you to fully take advantage of and utilize the resources allotted to you by your host. If even 1/10 of the sites on a server-farm took advantage of what they are paying for, the providers would go out of business.
My .htaccess files are being ignored.
This is almost always due to your AllowOverride directive being set incorrectly for the directory in question. If it is set to None then .htaccess files will not even be looked for. That is a good thing. If you have access to edit the httpd.conf, you should not use .htaccess files, ever. If your customers do need support for .htaccess, make sure that AllowOverride is set to something sensible (i.e.: Not All). Be certain it covers the directory you are trying to use the .htaccess file in. This is normally accomplished by ensuring it is inside the proper Directory container.
You can tell if this is your problem by adding nonsense text to your .htaccess file and reloading the page. If you do not get a server error, then Apache httpd is not reading your .htaccess file.
