Symbiosis is defined as an association between two organisms which is beneficial for both of them. Plant symbiosis with soil microorganisms is extremely important for plants as one of the mechanisms that enables them to survive under extreme conditions, such as low water and mineral content in the soil. There are two most important types of plant symbioses: mycorrhiza and symbiosis with nitrogen-fixing microorganisms. Mycorrhiza is an association between plants and soil fungi which enables more efficient water and nutrient uptake for the plant. Fungi are supplied with organic compounds which they cannot synthesize themselves. Nitrogen-fixing microorganisms also use organic compounds synthesized by plant, but their main task is conversion of molecular nitrogen from the atmosphere into compounds that can be used by plant. Symbiotic microorganisms can also be beneficial to other plants in the environment, not strictly for the ones with which they form symbiosis. Fungal hyphae improve soil capacity for retaining water and nitrogen-fixing bacteria enrich the soil with nitrogen compounds, making them available for the other plants. The importance of plant symbioses is well known and there are already many methods and procedures developed for the improvement of plant growth using microorganisms, for example in agriculture, floristry, wood industry etc. Further research of each type of symbiosis in order to improve methods of microorganism cultivation can significantly increase cultivation of many useful plant species, and the preservation of plant populations in areas that are otherwise unfavorable for certain plants species.