Several functions of arbuscular mycorrhizal (AM) interactions constitute the ecological services of the symbiosis which are the basis for their application as biostimulants. The bi-directional nutrient exchange between the mycorrhizal partners, the contribution of AM fungi to the quality of soils and plant responses to AM fungal colonization concerning their metabolic capacities and their morphology. Several aspects need to be considered for successful application of AM fungi. Firstly, the sites of plant production and their conditions must be advantageous for mycorrhizal functioning. Secondly, the genotype of the plant must support the positive functions of the symbiosis. Thirdly, inocula should be targeted to particular conditions by “training” or by combining them with other beneficial microorganisms. Finally, the market for mycorrhiza and mycorrhiza-based products has to be considered, in order to get the application of AM fungi more into the routine of plant production.