HHVM is quickly gaining popularity, and it is a pretty exciting time for PHP runtimes. Have you ever wondered what is going on beneath this slick, super-speedy engine? I wondered that myself, so I dived into the internals of HHVM, discovering a treasure trove of awesome stuff. In this talk, I will show you how HHVM works and how it all pieces together through a guided tour of the codebase. I will also show you a couple of ways to write your own incredible HHVM extensions.