Rudolf Carnap (1891-1970) and Otto Neurath (1882-1945) had a decisive influence on the development of the scientific world view of logical empiricism. Their relationship was marked by mutual intellectual stimulation, close collaboration, and personal friendship, but also by controversies that were as heated as they were rarely fought out in public. Carnap and Neurath were, in the words of Olga Hahn-Neurath, "like-minded opponents". The essays in this volume deal with these key thinkers of logical empiricism from different perspectives, shedding light on the complex development of one of the most influential philosophical currents of the twentieth century in the midst of dark times.