when employed in the context of an ASP.NET AJAX application, WCF services may actually work in a manner that is very similarly to ASMX services. By using the AspNetCompatibilityRequirements attribute, you state your will of having WCF and ASMX services to work according to the same model. One practical repercussion of this setting is that when a WCF service is activated, the runtime checks declared endpoints and ensures that all of them use the Web HTTP binding model.