The conventional understanding of microbes as causative agents of disease has led us to fear them and to consider them our deadly enemies. Much less appreciated are the central roles microbes play in shaping the environment and in maintaining plant, animal, and human health. All metazoan organisms – organisms that we can see with the naked eye – exist in lifelong partnerships with vast microbial communities. These “microbiomes” supply metazoans with essential life processes that are not encoded in nonmicrobial genomes. Recent work in microbiology has revealed that microbes, like metazoans, have specific body plans and sensory systems, that they can communicate with each other, and that they orchestrate collective behaviors. Investigations of these ancient yet enduring processes are uncovering the fundamental design principles of life. Microbes are also storehouses of new molecules, biochemical pathways, and materials with medical, industrial, and agricultural relevance. Scientists are harnessing these microbial products in efforts to confront humanity's most pressing problems. This essay explores the wonder, complexity, power, and utility of microbes in the twenty-first century.