This book is designed as an advanced guide for experiments in Modern Physics. It covers the Gamma Spectroscopy Experiment: the excited nuclear states, the interaction of gamma rays with matter, the general characteristics of photon detectors, the physical processes in semiconductor detectors, the Germanium detectors, the Experimental Setup, the detector resolution, the energy resolution with the HPGe Detector, the Photopeak Efficiency with the HPGe Detector, the Peak to Compton ratio, Data Analysis and Calibration, the determination of the unknown source, the determination of the position of the Compton and backscatter edges, the measurement of the resolution of the detectors, the measurement of the peak to Compton ratio as a function of the energy, the measurement of the intrinsic peak efficiency for 137Cs, etc. It is included the deduction of many formulas and the statistical analysis in order to clear the concepts and to get the concordance between the theory and the experiment. It is hoped that this book fills all needs of the students to get the fundaments of advanced experiments and to achieve the interest and motivation of the students for the real nature of the Physics.