Sergii Bulgakov (1871-1944) is one of the preeminent theologians of the 20th century whose work is still being discovered and explored in and for the 21st. A famous rival of Lenin in the field of economics, and, according to Wassily Kandinsky, "one of the deepest experts on religious life" in early twentieth-century Russian art and culture, Bulgakov, economist, publicist, politician, and later Orthodox theologian and priest, became a significant "global player" in both the Orthodox diaspora and the Ecumenical movement in the interwar period.This anthology gathers a collection of papers given at the international conference on the occasion of Bulgakov's 150th birthday at the University of Fribourg in September 2021. The chapters, written by established Bulgakov specialists, not least the keynote speaker Rowan Williams, former Archbishop of Canterbury (2002-2012), as well as young researchers from different theological disciplines and ecclesiastical traditions, explore Bulgakov's contribution to meeting the challenges of the modern world and to building bridges between East and West. The authors bring forth a wide range of new creative ways to critically engage with Bulgakov's theological worldview and cover topics such as personhood, ecology, political theology and trinitarian ontology.