I. The wisdom of a microscopic species. Evolutionary biology explains bacterial adaptability ; The ancestral microbiome ; Early factors influencing the microbiome ; Cracking the modes: from human genome to human microbiome ; Beyond bacteria: those other "omes" ; The microbiome hypothesis: the epigenetic role of the microbiome -- II. The microbiome's role in disease. The microbiome and gut inflammatory disorders ; The microbiome and obesity ; The microbiome and autoimmunity ; The microbiome and neurological and behavioral disorders ; The microbiome and environmental enteropathy ; The microbiome and cancer -- III. Manipulating the microbiome to maintain health. From association to causation: a new approach to microbiome compostion and function in disease development ; Preventive medicine: monitoring the microbiome for disease prediction and interception ; Treatments for disease: prebiotics, probiotics, synbiotics, and postbiotics ; Microbiome research in gut-brain axis diseases: psychobiotics ; Artificial intelligence, synthetic biology, and the microbiome ; Maintaining a resilient microbiome through old age -- Epilogue: Why studying our microbiome is important for our future.