| Troponin is a widely used biomarker in patients with cardiac disease. The use of troponin is well established in patients with suspected acute myocardial infarction (AMI), but troponin measurement is also used in other acute and nonacute settings. In patients with suspected AMI, early decision-making is crucial to allow rapid treatment and further diagnostic evaluation. Current guidelines recommend serial measurements of troponin with a cut-off concentration at the 99th percentile to triage patients in the emergency department. Newer, high-sensitivity assays for troponin enable the detection of distinctly lower concentrations. Using these assays and very low cut-off concentrations, several rapid diagnostic strategies have been reported to improve diagnosis in acute cardiac care. Furthermore, noncoronary and nonacute applications of troponin assays — for example as a biomarker in patients with heart failure, pulmonary embolism, or stable coronary artery disease — are on the horizon and might improve individual risk stratification. In this Review, we provide an overview on the development of high-sensitivity assays for troponin, and their application in patients with cardiac disease.