Now that PHP 5.3 has been released and is ready for production use, it's time to familiarize yourself with some of the new features that come with it. In this new tutorial from SitePoint they look at one of the more controversial additions - namespaces.
Namespaces are one of the most significant changes in PHP 5.3. They will be familiar to C# and Java developers, and they are likely to change the structure of PHP applications for the better. [...] Name collision problems can be solved with namespaces. PHP constants, classes, and functions can be grouped into namespaced libraries.
Thy look at namespace definition and some example code showing them in use - echoing out the results of a call to a constant, a function and a method.