The Ocsigen project aims to provide OCaml with a complete set of advanced tools for creating Web and mobile apps. It is used, for example, to build the Be Sport social network. Ocsigen contains, among other things, an OCaml to Javascript compiler (Js_of_ocaml), an extensible Web server, a widget toolkit, and a client-server framework (Eliom). Eliom allows you to write a client-server application in a single code, running on both Web browsers and mobile devices, with automatic and type-safe communication. In this workshop, you will learn how to build your first application. We will present the basic principles and many examples of use cases, showing how Ocsigen can save you a lot of time.