The article "Defining the Human Microbiome" by Ursell et al. reviews recent advancements in understanding the human microbiome, emphasizing the rapid development of sequencing methods and analytical techniques. The authors highlight how these advancements have expanded our ability to study the microbiome on various spatial and temporal scales, including long-term time series datasets. They discuss emerging concepts such as operational taxonomic units (OTUs), diversity indices, core versus transient microbiomes, and the possibility of enterotypes. The review also explores the dynamic interactions between the human microbiome and the environment, intrapersonal microbial diversity, and the role of the gut microbiome in digestion, nutrition, and health. The authors conclude by discussing the plasticity of the human gut microbiome and the potential for personalized medicine using the microbiome.The article "Defining the Human Microbiome" by Ursell et al. reviews recent advancements in understanding the human microbiome, emphasizing the rapid development of sequencing methods and analytical techniques. The authors highlight how these advancements have expanded our ability to study the microbiome on various spatial and temporal scales, including long-term time series datasets. They discuss emerging concepts such as operational taxonomic units (OTUs), diversity indices, core versus transient microbiomes, and the possibility of enterotypes. The review also explores the dynamic interactions between the human microbiome and the environment, intrapersonal microbial diversity, and the role of the gut microbiome in digestion, nutrition, and health. The authors conclude by discussing the plasticity of the human gut microbiome and the potential for personalized medicine using the microbiome.