On December 6, 1961, a contract was signed by which the research institute of the Wander AG in Freiburg became the Max-Planck-Institut fUr Immunbiologie. The transfer of ownership took place during a happy expansion phase of the Max-Planck­ Society in which a growing economy in Germany allowed the foundation of many new research institutes by the Max-Planck-Society and other organizations. Nevertheless, it was a remarkable event. The acquisition by an academic organization of an institute formerly operated by an industrial company was rather unusual, not to speak ofthe fact that not only the facilities but also the entire scientific personnel were taken over. Retrospectively, the 40 years of the institute in the Max-Planck­ Society can be divided into 2 very different phases of 20 years each. The first 20 years were characterized by a continuation of the research that had begun in the Wander institute and centered on the structure and function of the bacterial compound endotoxin. During the second 20 years, the institute more than doubled in size and developed into an interdisciplinary research center that focuses on the development and organization of multicellular systems by combining studies in two fields of research: immunology and developmental biology. th The 40 anniversary of the foundation of the Max-Planck-Institute was celebrated by a ceremony including a scientific symposium. The first part of this volume presents the lectures given at the symposium by six leading biologists.