Work on both the graphical user interface (GUI) and the conversational user interface (CUI) started at about the same time, about 40 years ago. The GUI was a lot easier to implement, and it made computing and information resources available to ordinary people. But over the years it has lost much of its simplicity and charm. The CUI has taken many more years to develop, requiring major scien- tific and engineering advances in speech, natural language processing, user-modeling, and reasoning, not to mention increases in cost-effective computation. But the infrastructure is now in place for the creation and widespread distribution of conversational interfaces. This talk describes some natural modes of conversational interaction and some of the supporting technologies that are now under development