Medicinal plants play a vital role in both traditional and modern healthcare systems due to their diverse therapeutic properties and active compounds. However, the role of microorganisms—particularly bacteria and fungi—in influencing the growth, chemical composition, and medicinal efficacy of these plants remained largely unexplored until recently. Recent research indicates a complex symbiotic relationship between medicinal plants and microorganisms, ranging from symbiosis to parasitism, with implications for plant biochemical properties and potential medical and agricultural applications. First: The Nature of the Symbiotic Relationship Between Medicinal Plants and Microorganisms 1. Symbiosis: In many environments, medicinal plants coexist with beneficial microorganisms such as mycorrhizae and plant growth-promoting bacteria (PGPRs). These organisms contribute to improved nutrient uptake, such as phosphorus and nitrogen, leading to enhanced plant growth and increased production of chemically active compounds like volatile oils, flavonoids, and alkaloids. 2- Defensive Stimulatory Interactions: Studies have shown that some microorganisms can stimulate medicinal plants to produce defensive chemicals that are antibacterial, antifungal, and antiviral. This type of interaction is known as "biostimulation," and it positively affects the plant's medicinal properties. 3- Competitive and Negative Effects: Conversely, some microorganisms may be pathogenic to the plant, negatively affecting growth or causing damage to plant tissues. However, even in these cases, these interactions can lead to the production of new substances or secondary compounds that may have medicinal importance. Secondly: Scientific and Practical Applications of the Interrelationship 1- Enhancing the Production of Active Compounds: By introducing beneficial microorganisms into the soil of medicinal plants, it has been possible to increase the concentration of active compounds. For example, using mycorrhizal fungi with mint plants led to an increase in the production of volatile oils with antiseptic and antimicrobial properties. 2- Bioculture of Medicinal Plants: This agricultural approach relies on using growth-stimulating microorganisms instead of chemical fertilizers and pesticides. This technology helps in producing safer and healthier medicinal plants, used in the pharmaceutical and food industries. 3- Biological Control of Plant Diseases: Some microorganisms can be employed to combat pathogens affecting medicinal plants, reducing the need for pesticides and protecting the environment. An example of this is the use of Bacillus subtilis bacteria to control gray mold in plants such as Echinacea. Al-Mustaqbal University, the leading university in Iraq.