At Particle Analytical, we have been working with determination of particle sizes for the pharmaceutical industry since 2000. Our customers have in general showed a large interest for an introduction to this area from a down-to-earth and practical perspective. The intended readers of this booklet are pharmacists and technicians working with determination of particles sizes. This booklet is not meant as a thorough introduction into theory behind determination of particle sizes, and only a limited number of references will be given: The booklet is primarily based on our own experiences and is a practical introduction to the area with a brief introduction to "why" and "how" in determination of particle sizes.