Holter electrocardiography (ECG) is a non-invasive test widely used to evaluate variety of cardiac arrhythmias. The ability to record changing dynamic cardiac electrical phenomena, that often are transient and of brief duration, is the major clinical advantage of Holter ECG. The Holter ECG historically became an important clinical diagnostic tool for the recording of cardiac arrhythmias, but its use has evolved to include signal-averaged ECG and linear or non-linear analysis of heart beat variability. These uses provides insight into the substrate, modulator and the trigger of arrhythmias. This chapter will review the advances in technology and interpretation of Holter ECG recording within the context of its application to cardiac electrophysiology and arrhythmias.