Myocardial infarction (MI) is a major cause of mortality and morbidity worldwide. Each year, an estimated 785,000 persons will have a new MI in the United States alone, and approximately every minute an American will succumb to one.1 In addition, MI has major psychological and legal implications for patients and the society and is an important outcome measure in research studies. The prevalence of MI provides useful data regarding the burden of coronary artery disease and offers insight into health care planning, policy, and resource allocation. The importance of accurately and reproducibly defining MI is therefore self-evident. The Third Universal Definition of Myocardial Infarction (MI) expert consensus document was published in October 2012 by the global Myocardial Infarction Task Force.2 This landmark document was cosponsored by multiple cardiovascular societies and included both updated definitions and a modified classification of MI that have important clinical, epidemiological, and research implications. We hereby present a critical overview of this important document and summarize its key recommendations.