Microbial ecology is the interrelationship between micro-organisms and their environment. Due to the high level of horizontal gene transfer among microbial communities, microbial ecology is also of importance to studies of evolution. The micro-organisms, by their omnipresence, impact the entire biosphere. They present important functions in the soil, as nutrient cycling and the degradation of pollutant. Additionally, soil micro-organisms promote other important functions for environmental sustainability. This book identifies the theory and applications of an integrated approach to microbial ecology of tropical soil.