In antenna arrays, mutual coupling between antenna elements is well known as an undesired effect, which degrades the performance of array signal-processing algorithms. The compensation of such an undesired effect has been a popular research topic throughout the years. Various approaches for mutual-coupling compensation have been developed, and they can easily be found in the open literature. In general, the mutual-coupling problems for a transmitting and receiving array are different, even if the physical geometry of the array remains unchanged. However, it seems that antenna engineers are not well aware of such differences in the analysis of receiving antenna arrays. In this note, the mutual-coupling problems in transmitting and receiving antenna arrays are revisited. The differences between the mutual coupling and mutual impedances for transmitting and receiving antenna arrays are explained. It is concluded that the mutual-coupling problems of transmitting and receiving arrays are in general different, and hence different mutual impedances should be used for mutual-coupling analysis and compensation.