The phyllosphere, the aerial habitat colonized by bacteria, yeasts, and fungi on plant surfaces, is a significant microbial ecosystem. Bacteria are the most abundant colonists, with populations ranging from $10^6$ to $10^8$ cells/cm². The leaf surface, a complex and dynamic habitat, is subject to rapid fluctuations in temperature, humidity, and nutrient availability. These conditions influence the microbial communities, which include various bacteria, fungi, yeasts, algae, and occasionally protozoa and nematodes. The composition of these communities varies over time and space, influenced by factors such as plant species, environmental conditions, and nutrient availability. Bacteria form large aggregates that can protect against desiccation and oxidative stress, and they can modify their microhabitat through the production of biosurfactants and plant growth regulators like indole-3-acetic acid (IAA). These modifications enhance nutrient availability and protect against environmental stresses. Additionally, the phyllosphere plays a crucial role in global processes, such as carbon and nitrogen cycles, and affects plant health. Understanding the interactions between bacteria and plants, as well as among bacteria, is essential for developing effective microbial control strategies and managing preharvest contamination of crops with human pathogens.The phyllosphere, the aerial habitat colonized by bacteria, yeasts, and fungi on plant surfaces, is a significant microbial ecosystem. Bacteria are the most abundant colonists, with populations ranging from $10^6$ to $10^8$ cells/cm². The leaf surface, a complex and dynamic habitat, is subject to rapid fluctuations in temperature, humidity, and nutrient availability. These conditions influence the microbial communities, which include various bacteria, fungi, yeasts, algae, and occasionally protozoa and nematodes. The composition of these communities varies over time and space, influenced by factors such as plant species, environmental conditions, and nutrient availability. Bacteria form large aggregates that can protect against desiccation and oxidative stress, and they can modify their microhabitat through the production of biosurfactants and plant growth regulators like indole-3-acetic acid (IAA). These modifications enhance nutrient availability and protect against environmental stresses. Additionally, the phyllosphere plays a crucial role in global processes, such as carbon and nitrogen cycles, and affects plant health. Understanding the interactions between bacteria and plants, as well as among bacteria, is essential for developing effective microbial control strategies and managing preharvest contamination of crops with human pathogens.