Early history of rheology, which established it as a separate field of study; work at University of Vienna on Albert Einstein's 1910 equation, Mark's contemporaries and colleagues (Frederick Eirich, Eugene Guth); move to North America, influence of World War II on technology of rheology, work at Canadian International Paper Laboratory and Polytechnic Institute; the Society of Rheology: inception and early days, course of development, officers and publications, Mark's presidency; remarks about the current status of rheology, advances since 1950, and orientation of future research.