The article first summarizes projects of quantitative sociological research into Czech religiousness, which were carried out from 1946 to 1989 (when, with the exception of 1950, religious affiliation was not a question on the census), and it subjects this research to a methodical critique. The author then discusses the institutional background of these research projects. Research into religious attitudes was carried out in 1946 by the recently established Institute of Public Opinion Research. After the Communist takeover, however, sociology was no longer an acceptable discipline, and State organs that were also working against religion took over this research task. Their research into 'objective religious factors,' conducted from the 1950s to the 1980s, considered only the decline in church-based religious feeling. More profound sociological research was made possible with the establishment of the Institute of Sociology at the Czechoslovak Academy of Sciences in the 1960s. Though this research was in the sway of the models of the period, that is to say, the 'sociology of the parish', it was relatively successful, methodologically suitable research (for instance into religiousness in North Moravia, 1963, with an attempt to expand it to the whole country), and met with a positive international response. It was doomed, however, by the policy of 'Normalization,' when the Institute of Sociology was merged with the Institute of Philosophy. Sociological research into religion was then entrusted to the Institute of Scientific Atheism, which was established in Brno. (The most important research that it conducted was into the religiousness of pupils and students of elementary and secondary schools in South Moravia, 1979.) Similar research was also carried out by the reorganized Public Opinion Research Institute in 1979, 1983, 1985, 1986, and 1989. Not one of these projects, however, can be considered rigorous, because the methods used were ideologically in the sway of the regime, it was not of sufficiently professional quality, and was palpably behind modern Western developments in the sociology of religion. More credible research, though limited for practical reasons, was provided by 'samizdat' and emigre sociology, which cast doubt on the idea of the automatic secularization of Czech society in connection with modernization and the dominance of Marxist thought. The development of truly unbiased research could take place only after the changes that began in late 1989. When interpreting earlier research and comparing results with contemporary findings on religiousness one must therefore bear in mind that it cannot be done without taking into account the conditions of the society and of the discipline in which the research was originally conducted, as well as the aims it was intended for.