mod_perl brings together the full power of the Perl programming language and the Apache HTTP server. You can use Perl to manage Apache, respond to requests for web pages and much more.
mod_perl gives you a persistent Perl interpreter embedded in your web server. This lets you avoid the overhead of starting an external interpreter and avoids the penalty of Perl start-up time, giving you super-fast dynamic content.
As you'd expect from the Perl community, there are hundreds of modules written for mod_perl, everything from persistent database connections, to templating sytems, to complete XML content delivery systems. Web sites like Slashdot and Wired Magazine use mod_perl.