This action filter attribute works with the HttpCorrelator (and HttpLogger) in AccidentalFish.ApplicationSupport.Owin to pull the correlation ID out of the header and set it in the call context. The reason this is necessary is that when hosting MVC in IIS a new call context scope is created between OWIN and the controller being invoked and therefore any call context values set in the OWIN middleware are not visible within Web API controllers and beyond. The easiest way to use this is to add it to the global filter set which in a typical MVC project is configured in App_Start\FilterConfig.cs: filters.Add(new HttpCorrelatorAttribute());