Airborne Particle Counters are widely used in Cleanrooms to monitor for signs of cleanroom air contamination and in most cases the particle count data is used to make critical process decisions. Today’s Portable particle counters have come a long way with the advent of laser diode technology, older generation cumbersome helium neon lasers also referred to as HeNe’s have been phased out in favor of smaller, lighter and feature packed new technology Portable Particle counters with touchscreens and automatic certification reports that comply to many of today’s Cleanroom Certification standards. In effect these devices have so much computing technology embedded that they really need to be validated to ensure they meet your process requirements and with so much focus on data integrity and the FDA’s ALCOA approach this paper takes a deep dive into Particle Counter technology more than we have ever seen previously which will help to assist decision makers in making informed choices when considering which option/model is best for their process when data integrity is of paramount importance to them. It is important to also acknowledge the advantages of an ISO 21501- 4 calibration. ISO 21501-4 is a major particle counter calibration standard and one of the most complete guidelines and it is important that particle counters are calibrated to meet this standard as this calibration allows for better accuracy and reliability which in turn mitigates data integrity issues by verifying count data is as accurate as it can be, therefore it is important to understand the relationship between ISO 14644-1:2015 and ISO 21501-4:2007. Overall the objective of this article is to increase your knowledge in Particle Counting technology so you are more aware and experienced as particle counters play such an important role in the front line of defense against contamination in your Cleanroom.