In the popular imagination, historical relations between the Roman Catholic Church and modern science are best epitomized in the case of Galileo Galilei. Condemned in 1633 for advancing the theory of a moving earth and a stationary sun, he was only exonerated in 1992. Yet apart from relatively few and specialized studies, there have been no extensive historical treatments of Catholic attitudes toward science after Galileo. This is the first general history of the reactions of the Roman Catholic Church to developments in the natural sciences from about 1800 to the dawn of the twenty-first century.

While Galileo's heliocentric universe had challenged the "inerrancy" of the Bible, Darwin's theory challenged the direct and immediate creation of the first humans. Through O'Leary's cast of characters—popes from Pius IX to John Paul II, polemicists like Thomas Henry Huxley and Irish physicist John Tyndall, and Catholic apologists and scientists like St. George Jackson Mivart—we get a clear picture of the back and forth volleys between representatives of the scientific and ecclesiastical establishments as well as within each of those establishments. Besides evolution, a wide range of other issues receives attention, including agnosticism, biblical criticism, the philosophy and professionalization of science, the nature of Catholic dogma vis-à-vis science and of intellectual freedom vis-à-vis faith and ecclesiastical authority. Many of these issues achieved a certain resolution in the years before and after the Second Vatican Council. However, toward the end of the twentieth century, new issues facing the church and global society emerged with a new variety and urgency, with environmental concerns, on the one hand, and portentous developments in the biological sciences, on the other, including contraception, "in vitro" fertilization, gene therapy, experimentation on embryos, and organ transplantation. O'Leary explains the intricacies of all of these issues clearly and fairly, though their ultimate resolution may take decades to achieve.