The human body has 10-100 trillion microbes living on it, making it one giant super-organism. Since the first link between microbes and diseases was made, people have been advised to wash there hands. Scientists, however, have recently started to investigate more closely how the microbes that call the human body home affect our health. While some microbes cause disease, others are more beneficial, working with our bodies in many subtle ways.As with the human body, microbes throughout the world play important roles in their ecosystems. In spite of being extremely small, the sheer number of microbes living on the planet have large effects on the cycling of nutrients and compounds, both essential for the survival of all organisms. To survive in so many types of habitats, microbes have evolved a great number of mechanisms to find energy, digest food and reproduce. Scientists use these skills in a number of ways, including agriculture, energy production, medicine and warfare.