Publisher Summary This chapter describes the works of the theologian, philosopher, and scholarly encyclopedist, Father Pavel Aleksandrovich Florensky. Florensky underwent a spiritual conversion in 1899, which was part of a countervailing movement that began around 1900 and has become known as the Russian religious philosophical renaissance. It saw some leading intellectuals turn, or return, to the Russian Orthodox Church. Pavel Florensky was to become one of the most important figures in this movement. In addition to the study of mathematics, Florensky attended the lectures of the well known philosopher L.M. Lopatin from the Faculty of History and Philology and visited the seminar of the important philosopher S.N. Trubetskoy. He was intensely interested in art history and poetry. Florensky considered nomena to exist in a special space that is in an “inverted,” “reversed,” or “imaginary” relationship with physical space—both worlds, the physical and the spiritual, are inseparable. Florensky interpreted them as lying on the two sides of a single surface. Thus, Florensky conceptualized that the two sides of a symbol, the phenomenal and the nomenal, are obtained from each other by literally turning inside out. Florensky gave a special place to mathematics. Above all, he regarded mathematics as a means for understanding the structure of complicated phenomena in different fields, including philosophy and theology.