A literature survey was conducted to collect mineralogical data of Canadian soils. In the past 40 years, clay mineralogical data of varying precision have been reported for approximately 1200 samples from more than 380 pedons. Based on the data, (1) the distribution of clay minerals was examined physiographically, (2) an investigation was made to relate specific changes in clay minerals of pedons within a physiographic region to taxonomy, and (3) a comparison was made of the clay mineral alteration in the pedons of the same order in different physiographic regions. The results indicated that virtually no or minor alterations of clay minerals had occurred in pedons of many Canadian soils with the exception of Podzolic soils and to a limited extent, Brunisolic, Luvisolic and Gleysolic soils. In the Podzolic soils, chlorite disappeared or diminished in surface horizons, and micas and possibly some chlorites were transformed by hydration into partially or fully expansible clay minerals. For general soil clay mineral characterization, the analyses of one subsoil sample of a pedon would appear to be adequate for most soil orders. However, clay mineralogy has a potential to go much further in distinguishing minor changes and subtle differences in clay minerals. Such information would be useful in specific studies of soil development and in assessing trends in early stages of weathering. The current priorities of soil clay mineralogy in Canada should be improvement of methods of quantification and increasing the standardization of methodology and interpretation of results.