The Consortium of Metabolomics Studies (COMETS) brings together prospective cohort studies that meet two criteria: (1) the cohort includes at least 100 participants with identified metabolites measured in blood (plasma or serum) using mass spectrometry (MS), nuclear magnetic resonance spectroscopy (NMR), or other high-throughput analytical technology (e.g. coularray), and (2) cohort participants are followed after blood collection for chronic disease outcomes (e.g. mortality, cardiovascular disease and cancer). As of June 30, 2017, 42 prospective cohorts from Asia, Europe, North America and South America have joined COMETS. The aim of COMETS is to enable the study of metabolomics of a range of diseases and health statuses in large prospective studies that enable replication and adequate power for exploring causal effects (for e.g. with genetic instruments), sub-group analyses, non-linear associations and rare diseases. It also brings together a multidisciplinary group of international researchers to share methodological approaches and developments in the field of metabolomics epidemiology.