Since its introduction as a clinical investigative tool, the 12-lead electrocardiograph (ECG) has been the gold standard for recognition of cardiac arrhythmias. The resting 12-lead ECG, however, gives only a rhythm snapshot in time, whereas arrhythmias maybe short-lived, paroxysmal and even asymptomatic making documentation in many patients very difficult. To overcome this, ambulatory ECG monitoring has been developed as a means of recording the ECG in patients over a set period of time, whether it be short-, medium- or long-term. With the miniaturisation of recording devices and advances in solid state technology, there has been a recent revolution in hardware design, so that the boundaries between these time-dependent devices have become blurred. Not surprisingly, the indications for monitoring have broadened as the quality and range of monitoring devices have become available. In this review, the indications for ambulatory ECG monitoring with emphasis on non-arrhythmic indications such as ST segment analysis, heart rate variability, signal averaged ECGs, diurnal QT and QTc analysis, obstructive sleep apnoea and vectorcardiography will be discussed. Also, the types of electrode systems used, lead placement, monitoring hardware, data collection, analysis and presentation as well as cost effectiveness of the investigation will be covered.