Bayesian methodology differs from traditional statistical methodology which involves frequentist approach. Bayesian methodology was introduced by Thomas Bayes (Statistician and minister at the Presbyterian Chapel) during the 18th Century. Bayesian methodology is now widely being used due to its simple, straightforward and interpretable characteristics of probability values and the efficiency of modern day computer systems. Bayesian methodology is now being used in the field of clinical research, clinical trials, epidemiology, econometrics, statistical process control, marketing research and statistical mechanics. It also used in the emerging field such as data science (machine learning and deep learning) and big data analytics. The book provides an overview of Bayesian methodology, its uses in different fields with the help of R statistical open source software. It is recommended to refer author's book on Application of Statistical Tools in Biomedical Domain: An Overview with Help of Software and Essentials of Bio-Statistics: An overview with the help of Software if you need to familiarize yourself with the basic statistical knowledge.