ABSTRACT Microbes continue to live on and within human beings. Intestinal microbial imbalance has a close relationship with human health and disease. This review article targets on the communication between human microbiome and host in order to provide an overview of the microbial role in biological processes and in major human diseases such as infectious diseases, liver diseases, gastrointestinal cancers, metabolic diseases, respiratory diseases, mental or psychological diseases, and autoimmune diseases. Hence research is necessary for understanding the role of microbiome in health and disease which pave the way for treatment approaches in clinical practice.