The Log property of QuartzSchedulerThread is null in most (if not all) situations I have tried. The problem seems to be that QuartzSchedulerThread() constructor is never called. Instead the child class QuartzThread constructors are called by the framework. The fix is to have QuartzSchedulerThread expose the same constructors as QuartzThread to assure that every instantiation of QuartzSchedulerThread creates the readonly log object.