A fast-growing field of research focuses on microbial biocontrol within the phyllosphere. Phyllosphere microorganisms possess biocontrol capacity with good range of adaptation to the phyllosphere environment and inhibit the expansion of microbial pathogens, thus sustaining plant health. These biocontrol factors are often categorized in direct, microbe-microbe, and indirect, host-microbe, interactions. This review gives an summary of the modes of action of microbial adaptation and biocontrol within the phyllosphere, the genetic basis of the mechanisms and samples of experiments which will detect these mechanisms in laboratory and field experiments. Detailed insights in such mechanisms are key for the rational design of novel microbial biocontrol strategies and increase crop protection and production. Such novel biocontrol strategies are much needed in today’s world to ensure sufficient food production to feed the growing world population.