For our planet to be still habitable, we must protect human health, the health of all living being and environmental health, integrated in one only health, in a loving bond. This book starts with an historical path of events in which toxic contaminants have proven to be risky for health. Then, it develops on how bird are sentinels of health risks in wild environments, both agricultural and urban; the way in which fishes reflect the origin and impact of contaminants in the water resources; the way in which bovines may warn about the quality of agricultural environments where our food is produced, and lastly, the way in which dogs are protagonists in medicine, due to the studies realized on them are also helpful for human health. The knowledge of animal health warns us about risks for human health and environmental health, and the links between the three of them, in a reciprocal way.