Unstable angina and non-ST-segment acute coronary syndrome represent a frequent and serious presentation to the emergency department. While most patients present with chest discomfort, atypical presentations warrant that clinicians maintain a high index of suspicion. This review summarizes the present nomenclature, definitions, and pathophysiology for this high morbidity disease process. The rapid acquisition of an electrocardiogram and serial cardiac troponins are mainstays of diagnosis. Also outlined is an approach for initial assessment, high-risk ECG findings, risk stratification, biomarker strategies, and subsequent stabilization. Once diagnosed, treatment options for these patients aim to halt continued ischemia and resultant necrosis. These therapies may include agents such as supplemental oxygen, nitrates, anti-platelet agents, beta blockers, anti-coagulation, anti-thrombin and statin therapies in appropriate settings. Caution should be exercised when dosing high-risk patients for bleeding such as those who are elderly or who weigh less than 60kg. Emergent angiography is reserved for patients who develop hemodynamic instability, cardiogenic shock, pulmonary edema, persistent angina refractory to medical therapy, and sustained arrhythmia. This review contains 2 figures, 12 tables, and 64 references. Keywords: acute coronary syndrome, unstable angina, myocardial infarction, troponin, electrocardiogram