As in most other aspects of its behavior, the surfaces and interfaces of Hgl-xCdxTe are anomalous when compared to the bahavior of other better-understood semiconductors such as Si and the 3-5s. The thrust of this paper will be, first, to outline and, as far as possible, to document these differences. Second, we will make tentative suggestions as to the reason for this difference, indicating the data and reasoning underlying these suggestions. This leads inescapably to the third and very important part of this paper-an attempt to identify the key areas in which we lack critical knowledge and to suggest approaches that may produce such knowledge. Here, as elsewhere in this paper, we attempt to indicate how other work reported at this meeting fit into the overall picture which is beginning to emerge. The fourth section of this paper will give an overview of the passivating overlayers placed on the surface of Hgl-xCdxTe and the results obtained from them. It will also attempt to relate these results with the thoughts, questions, and concepts developed earlier in this paper.