Mycorrhizal fungi represent crucial partners for plants in the soil, entering into mutualistic symbioses that significantly enhance plant growth and health. Mycorrhiza is a mutualistic symbiosis between fungi and plant roots, enabling better access to nutrients and water. Historically, this phenomenon was recognized in the late 19th century and is now of key importance for sustainable agriculture. Mycorrhizal fungi absorb mineral nutrients from the soil and transfer them to plants while receiving carbohydrates produced by photosynthesis in return. There are several types of mycorrhizae, including arbuscular, ectomycorrhizae, and ericoid mycorrhizae, each with different characteristics and roles in the ecosystem. Mycorrhizal fungi play a crucial role in maintaining ecosystems. They improve soil structure, increase biodiversity, stabilize ecosystems, and help plants adapt to different environmental conditions. Fungi colonize plant roots through spores or hyphae, forming specific structures for nutrient exchange. Plants release carbohydrates that fungi use as an energy source, while fungi absorb mineral nutrients from the soil and transport them to plants. Mycorrhizal fungi increase nutrient absorption, secrete growth hormones and enzymes, and protect plants from heavy metals and salts. The increased nutrient absorption is especially important for phosphorus and nitrogen, which are essential for plant growth. Mycorrhizal fungi induce numerous physiological changes in plants, resulting in the strengthening of their defense mechanisms. The activation of defense mechanisms includes the production of phytoalexins, strengthening of cell walls, and activation of defense genes, which increases plant resistance to pathogens. This paper explores the wide range of beneficial effects of mycorrhizal fungi, particularly in the context of their role in nutrient absorption, secretion of growth hormones and enzymes, protection from heavy metals and salts, and enhancement of plant resistance to pathogens.