This comprehensive book provides a detailed introduction to the principles of particle detectors used in physics, biology and medicine. Introductory chapters review the interactions of particles and radiation with matter, introduce the principles of detector operation and describe and define different types of measurement and their units. The main body of the book encompasses all currently used detectors and counters. Each description covers basic principles, potential uses and limitations. The scope of the book includes detectors for ionization and track measurement, methods for time, energy and momentum measurement, and for particle identification. Two chapters are dedicated to electronics (readout methods, monitoring, data acquisition) and data analysis. A final chapter gives examples of detector systems. The book concludes with a detailed glossary of terms, tables of units and physical constants and a detailed reference list.