Proterozoic time produced much of great interest to geologists, and was of tremendous economic import to the people of Canada and the United States. Most of the iron deposits of the Lake Superior district, the Michigan copper deposits, the enormously important Sudbury nickel-copper-platinum deposits, the spectacular silver deposits of the Cobalt district, and all of the important uranium ores in the Shield area are considered to have formed during this period in geological time. Proterozoic rock groups include those Precambrian rocks which are least deformed and metamorphosed. Because of their important economic deposits, they have been examined in great detail in certain localities. The results of such examination, and of others which were for reconnaissance only, are summarized in this volume of the Royal Society of Canada. Suggestions are made for revision of previous interpretations of Precambrian history, and the terminology which grew out of them. Three papers deal with problems arising from the current use of the term Proterozoic, and with possible changes in its use to bring it more into accord with the facts. Contributors to this volume are: E.M. Abraham, Robert Bergeron, R.G. Blackadar, I.C. Brown, G.H. Charleswood, J.F. Davies, K.E. Eade, W.F. Fahrig, R.M. Farquhar, James E. Gill, H.C. Gunning, J.M. Harrison, D.F. Hewitt, W.W. Moorhouse, J.E. Reesor, S.M. Roscoe, R.D. Russell, James E. Thomson, Robert Thomson, L.J. Weeks, Alice E. Wilson, J.T. Wilson, G.M. Wright.