The 4th edition of the Universal Definition of Myocardial Infarction (MI) recommends measurement of cardiac troponin (cTn) T or I for the diagnosis of MI due to their absolute cardiac tissue specificity. In this MI definition, values exceeding the 99th percentile of a healthy reference population distinguish between detectable troponin due to physiological cell turnover as opposed to pathological myocardial injury. In clinical routine, high-sensitivity (hs) troponin assays that allow earlier diagnosis of MI and detection of myocardial injury that would have escaped detection due to the lower sensitivity of previous assay generations are increasingly used. While the 2015 European Society of Cardiology (ESC) guidelines already recommend a re-testing of cTn after 3 h, if an hs-cTn assay is available, faster protocols that reassess hs-cTn after 60–120 min are increasingly performed, since these protocols allow faster patient disposition, increase discharge rates from the emergency department (ED), and are at least as safe as the standard protocol for the guidance of discharge after rule-out. However, decision cut-offs are lower than the 99th percentile and concentration change criteria depend on the individual hs-cTn assay and protocol used. The following article provides an overview of the recommendations of the 4th universal MI definition as well as the current 2015 ESC guidelines on cTn and other potential biomarker candidates for patients presenting with suspected acute coronary syndromes. Limitations and areas of controversy are discussed.