This book explores the subject of recommendation systems in-depth, which provide users with personalized product or service recommendations based on their previous searches or purchases. Various apps, such as question log mining, social networking, news recommendations, and ads, have adapted to propose device approaches. This book synthesizes both basic and advanced subjects in a field of study that has now reached maturity. While this book serves mainly as a textbook, it would also cater to scholars because of its emphasis on case analysis.