Languages are probably the most flexible tools that humans have evolved. Dialogue is the interactive usage of a mutually agreed language between the communicators to exchange information. However there are many problems and even barriers to successful human communication, and still more for man-eomputer dialogue.In the past computer ergonomics had tended to concentrate more upon hardware and environment issues, but in the last 3 to 5 years there has been growing attention to the software,organizational and cognitiveaspects. Some of the relevant studies will be mentioned to illustrate the nature and flexibility of human conversation, the types of contribution available from compuler ergonomics, and the prospect towards guidelines for dialogue design.