This document discusses biomarkers, which are measurable indicators of biological states or processes. Biomarkers can take various forms including cellular characteristics, metabolites, molecular variations, or physical features. They can be used for diagnosis, disease staging, monitoring disease status, and predicting or monitoring responses to interventions. Examples of biomarkers include electrocardiograms, PET scans, serum chemistries, and pulmonary function tests. Biomarkers are also used in drug development to evaluate safety and activity in animal models, determine optimal human dosing, and monitor responses and toxicity. Companies are working to develop biomarkers for applications in drug research and development.