What are the differences between wcf and asmx

Instead of attributing the specific method like we do in ASMX, in WCF we attribute the Interface.  Programming to an Interface is a good thing and the reason this is done is to loosely couple the host of the service from the implementation.  Doing this opens the door for hosting WCF services not only in IIS but console apps, Winforms, WPF, etc.  Since we’ve programmed to a contract (which is just an Interface), any class that implements the Interface can be a service.  This is powerful.  This is powerful because how we expose this service is up to us (again it is all about configuration). 
WCF provides developers the ability to write code once and repurpose their code as needed.