Oh no! Harry Potter, the hero from the J K Rowling’s wizarding universe, has been cursed by the super-villain, Lord Voldemort, and now he is trapped inside the Internet! Harry knows Parseltongue, which means that he can talk to snakes. Incredibly, Parseltongue also happens to be a Turing complete programming language! In order for Harry to escape from the Internet, we need to transpile Parseltongue into JavaScript. In order to do that we need to learn all about Abstract Syntax Trees and how to use them to manipulate code. This talk goes through the details of these magical data-structures, and all about language transformation, including lexing, parsing, code generation and creating source maps.By the end of the talk, attendants should have an idea of how ASTs work, how they are used in code transformation, and how they can be used to manipulate and interrogate code at a structural level.