Assessment of people's views with an emphasis on sociological aspects is mainly associated with the tradition of the European public opinion research. American authors introduced empirical and socio-psychological approaches to this field of study. Hadley Cantril was one of those who pioneered "scientific" public opinion research inspired by George Gallup. This paper reviews Cantril´s work, recalling some of his most important theoretical and methodological findings and empirical projects, to conclude that his studies remain a rich source of knowledge for all present-day and future public opinion researchers.