Measurement of the mutual intelligibility of dialects of a language is discussed. The focus is on several theoretical constructs in measurement, illustrated with data from an earlier study of the mutual intelligibility of 17 Chinese dialects. Measurement procedures are also explained. It is proposed that mutual intelligibility is based on the ability to categorize things and recognize patterns, and that phonological correspondences between source and target dialects fall into two categories: common (communication signals) and less common (noise interference). Further, these patterns of correspondence (signal and noise) can be weighted according to the characteristics of their occurrence. Computation of indexes of mutual intelligibility using these weightings, made at the level of the syllable-word in Chinese, is explained. Appended materials include: calculations for the mutual intelligibility of initial consonants, vowels, endings, and tones of two Chinese dialects, those of Beijing and Jinan; a chart illustrating degree of dialect affinity of 17 Chinese dialects based on mutual intelligibility; a chart illustrating dialect affinity based on genetics relations of initials, finals, and tones. Contains 29 references. (MSE)