Symbiotic interactions between plants and mycorrhizal fungi have a major impact on plant growth, development and evolution. Among them, the ectomycorrhizal (ECM) symbiosis formed between a large variety of phylogenetically diverse fungi and trees, and the arbuscular mycorrhizal (AM) symbiosis involving almost all land plants and the monophyletic Glomeromycota, are critical players of most ecosystems. Beyond their ecological functions, these associations offer a unique opportunity to improve the productivity and sustainability of current forest and agricultural systems. Over the last two decades, genetics conducted in model legumes has allowed the identification of a first set of genes and molecular mechanisms required for the efficient establishment of the AM symbiosis but also highlighted how scarce and incomplete our understanding of this association is at the molecular level. The 2nd international Molecular Mycorrhiza Meeting (2nd iMMM) brought together researchers who work on the molecular characterization of AM and ECM symbioses in a variety of contexts including root colonization, cell dynamics, nutrient exchange and metabolism, molecular evolution, genomics, effectors, plant–fungal communication, hormonal regulation or signal transduction. During this year's meeting many presenters outlined novel discoveries, concepts and models that are likely to take the research on mycorrhizal associations into new realms.