This chapter will explain the basis of services in the Symfony2 framework. A service is an essential and core concept in Symfony2. In fact, most of the framework itself is just a big set of predefined services that are ready to use. As an example, if you just set up a new installation of Symfony2, from your project root, you can type php app/console container:debug to see the full list of services currently defined in your application. As you can see, even before we start writing anything for our application, we already have almost 200 services defined. The php app/console container:debug <service_name> command will provide information about a specific service and will be a useful command to refer to throughout the book.