Intra-arterial blood pressure measurement is considered to be the gold standard for blood pressure monitoring of hemodynamically unstable patients in intensive care unit (ICU), intraoperatively and during perioperative period. Arterial pressure waveforms are directly transmitted through the column of fluid in the tubing that connects arterial cannula to the pressure transducer. Transducer converts the pressure waveforms into an electrical signal, which is further processed and amplified by a microprocessor and converted to visual waveform display on the monitor. Arterial cannulation and invasive blood pressure monitoring are a common procedure in various perioperative and critical care settings. Components of intra-arterial blood pressure monitoring system, waveform analysis, normal arterial pressure waveforms, difference in waveforms according to site of insertion, beat-to-beat variability in arterial pressure waveform are some other important topics also covered in this chapter.