Complex communities of microbes live on and in plants, humans and other animals. These communities are collectively referred to as the microbiota or microbiome. Plants and animals evolved to co-exist with these microbes. In mammals, particular kinds of alteration of the microbiome (dysbiosis) are associated with loss of health, most likely due to loss of microbial metabolites, signalling molecules, or regulators of host pathways. Modern life-style diseases such as Inflammatory Bowel Disease (IBD), Irritable Bowel Syndrome (IBS), type 2 diabetes, obesity and metabolic syndrome have been linked to dysbiosis. These multifactorial diseases involve multiple risk factors and triggers, depletion of certain gut microbiota species being one of them. Live Biotherapeutics operate by restoring microbial products or activities in affected subjects. They are being developed as adjuncts, alternatives or new treatment options for diseases that affect a growing proportion of global citizens., (© 2017 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.)