Increasing evidence, mostly from preclinical studies, indicates a role for the gut microbiome in modulating brain development and function across the lifespan. This pinpoints the microbiota-gut-brain axis as a potential target for influencing mood and behaviour, to impact conditions such as anxiety and depression, as well as for preventing or treating brain-related conditions, including Parkinson’s disease, Alzheimer’s disease, schizophrenia and autism. One of the current challenges is the translation of these insights into the clinical context.