Within the last decade, our understanding of the role of the intestinal microbiota in health and disease has rapidly increased due to significant advances in next-generation sequencing technologies. Scientists have discovered more and more gut microbes with supposedly "beneficial" roles for human health and are starting to identify the underlying mechanisms. In this review, we summarize the latest knowledge about the human intestinal microbiota, including the intestinal bacteriome, virome and mycobiome. We discuss the function that recent studies attribute to the intestinal microbiota in preventing or controlling selected diseases and present recent research on biotherapeutic approaches to control these diseases.