Medicinal plants have represented accessible and highly bioavailable remedies in traditional therapeutic and preventive practices of numerous populations worldwide. Veterinary treatments based on medicinal plants are also widespread, mainly targeting the control or prevention of parasitic diseases. Scientific support of the immune-stimulating efficacy of plants or their extracts in animals is less documented. The immunological activity of alcoholic plant extracts was investigated in numerous animal classes, starting from Pisces, through Reptilia and Aves and reaching Mammalia, envisaging their effects on innate and adaptive cell-mediated immunity, which the authors mean to share in this chapter, also providing a comparison of variable reactivity within and between the classes.