Nowadays, there is a vast amount of data available for analysis, which if analyzed and interpreted accurately can yield valuable knowledge and key insights into customers¿ needs. This book, will focus on the application of data mining analysis in the telecommunication sector and how this can be used to help in predicting and identifying customers that might leave a telecommunication provider to go to the company¿s competitors (churn). When customer churn is predicted accurately, telecommunication companies will be more able to take proactive decisions to ensure that customers stay with the company i.e. customer retention.