Relaxation Phenomena in Condensed Matter Physics features various methods for spectroscopy techniques presented in this book and the relation of these techniques to correlation functions. This book aims to present the similarities and differences between different studies of the relaxation phenomena and to come up with a unified theoretical approach. This text is divided into two major parts, A and B. Part A deals briefly with several spectroscopy experiments and how they can be analyzed in terms of correlation functions. Spectroscopy techniques are likewise discussed in this part. Part B focuses on the stochastic theory of the said correlation functions, where each stochastic model is situated in the context of a physical process. The result of the calculations is then related to one of the experiments featured in Part A. These stochastic methods provide a simple mathematical framework in analyzing relaxation phenomena that can be related to diffusion process. This book is targeted to graduate students who have already taken quantum and statistical physics and is a good reference to students, scientists, and researchers in the field of condensed matter physics.