Theoretical biology emerged as a discourse among biologists from a variety of different experimental disciplines and some philosophers and physicians during the early decades of the 20th century. This discourse was centered around the conceptual, epistemological, and methodological foundations of biology as well as the relation of biology to physics and metaphysics (the problem of the autonomy of biology), mathematical modeling of biological processes (such as regulation, differentiation, inheritance, and organic transformation), and the representation of biological knowledge. It engaged many of the foremost biologists of Europe (Germany, The Netherlands, Austria, Russia, and Britain) and, to a lesser extent, the United States. Vienna has traditionally been a fertile ground for discussions related to theoretical biology. Several prominent members of the Vienna Medical School, arguably one of the leading centers of Medicine at the turn of the 20th century, had a strong interest in conceptual problems of biology and medicine; research in experimental and theoretical physics explored problems related to biology; Ernst Mach’s approach to history and philosophy of science was based on an evolutionary (or adaptationist) approach to knowledge. Last but not least, the Vivarium, an initially private Institute for Experimental Biology fostered research into the theoretically relevant problems relating physiology,development and environmental modification. On the year of the 100th anniversary of the foundation of the Vivarium the workshop will explore the historical roots as well as the legacy of theoretical biology in Vienna. It will focus on the history of the Vivarium and investigate the careers and contributions of important figures associated with it (Przibram, Kammerer, Exner, Weiss, von Bertalanffy). But the workshop is also intended to raise larger themes and open up fresh perspectives for theoretical biology in the 21st century. There will be papers that place the Viennese tradition in the larger context of modeling biological processes, explore the history and future perspective of research into the role of the environment in development, and analyze the significance of extra-university settings and research institutes in both the past and present. Finally, today´s role of theoretical biology in integrating the life sciences will be analyzed.