In Joomla 3, once you enable Search Engine Friendly URLs (obviously for better Jooml Search Engine Optimization), you will probably get index.php in your address. Something like www.yourdomain.com/index.php/about-us.

If you want to remove the index.php, it is very simple. Besides enabling the Search Engine Friendly URLs, you'll also need to enable URL rewriting. 

Quick recap:

• Go to Global Configuration
• Enable Search Engine Friendly URLs
• Enable URL rewriting

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