This chapter will expose the founding acts of the three main pioneers of immunity, when neither the science of immunity nor the name that will designate it yet existed. “The attenuation of germs”, which Louis Pasteur made the basis of vaccination, the “Messina experiment”, by which Ilya Metchnikov sealed the fate of immunity by assigning to phagocytes the task of protecting the organism “against harmful intruders”, and the description of antibodies, which Paul Ehrlich made “the magic bullets” of immunity, are the foundations on which the science called immunology, rests.