Holter monitoring represents a valuable diagnostic tool to document intermittent arrhythmias in the work-up of, for example, syncope, presyncope, collapse, falls, dizziness, stroke, palpitations, and a rapid heartbeat. In addition, it may help in the diagnosis of intermittent ischemia and channelopathies, particularly in the form of 12-lead Holter monitoring. Continuous ECG registration typically lasts from 24-48 h. The use of Holter monitoring is limited in patients with rare symptoms (< 1 × per month) and in recordings full of artifacts. The interpretation of a Holter recording combines an automatic analysis with a manual reassessment. The clinical relevance of many arrhythmias can only be considered together with symptoms and activity of the patient at the time of the event. Therefore, a patient diary accompanying the ECG recording is crucial. Systematic assessment of the ECG recording and knowledge about a number of pitfalls in Holter monitoring can optimize the interpretation of the recording.