The exposure to radon is the second cause for lung cancer after smoking, and reason number one for never smokers. The exposure can be evaluated by measurements only. This book is focused on the methodology of radon and radon progeny measurements and its application in case studies. In chapter II the theory and application of diffusion chambers with solid state nuclear track detectors for integrated Rn-222 measurements are considered. Mathematical expressions for the distribution of Rn-222 progeny in the chamber’s interior are derived. Chapter III is focused on measurement of radon progeny. The general mathematical algorithm for grab sampling measurements of Rn-222 and Rn-220 progeny is described. Further, a method for integrated measurements of the individual concentrations of Rn-222 and Rn-220 short-lived decay products is presented. Chapter IV deals with case studies. The radon monitoring data for underground miners in Bulgaria is summarized and study of the correlation between radon progeny exposure and bronchial dysplasia in miners is presented. Three studies in radon-prone areas are discussed. The book should be useful for professionals interested in radon.