The gut microbiome is fundamental to human health and development. Altered microbiomes have been associated with many diseases. However, variation between individuals, environmental effects, and a lack of standardization across studies makes differentiation between health and disease challenging. Large-scale population cohorts in different countries will be required to match disease subjects with healthy controls, whereas standardized, reproducible pipelines for analysis are required to compare findings between studies. Despite this, several conditions have already demonstrated great promise for developing microbiome-based biomarkers as well as providing a gateway into integrated personalized medicine.