PERL: including files

I am wondering how I can include external files in a perl script. I'm currently working on a website, and I'd like to put my menu items in a subroutine for example, and put that in another file such as menu.pl. That way, I can call the subroutine from each page (such as news.pl), and if I want to add a menu item, I can add it in the menu.pl file and it would be changed on all pages of the website.
However, I have no idea how to accomplish this. Any suggestions?

Thanks

look up require

fyi - it's Perl , not PERL

Ah.. thanks for the tip! very useful.. At least now it'll be a bit more flexible..

cheers