During the past decades, especially after the World war II, the Operations Research has played an important role in economic and social development of countries. From the early days, OR, considered utilising mathematical models to solve military problems. Gradually, success in OR projects encouraged professionals from other disciplines to use its techniques and tools in their own fields. Library and information Sciences/Studies (LIS) was one of the domains affected by the OR and used it severely. This book is in fact an effort to inject OR in LIS, in a manner that it could be used by academic librarians. It has a systematic structure through which understanding basics of the OR would be possible for librarians, especially those who don't have sufficient knowledge and experience in mathematics. At first, Or is defined and its evolution is illustrated. Then, Or methodology is introduced and its characteristics are discussed. The most important techniques of the OR have been argued throughout the book from absolute to probabilistic and mixed models. There are little works in the area of mathematics with this general approach to the OR. Most of them trace one of the techniques of OR; for example, linear programming. Therefore, the main feature of the present work is that it has an overview on the OR and tries to support discussions with real examples from the field of LIS. While examples have been provided everywhere to simplify the matter; the last section has specifically been dedicated to a more explanation of the areas of OR application in the field of library and information services. You all librarians, need this book seriously. First of all, you have to be familiar with the OR as a mathematical approach for handling the daily issues. Apart from this obvious statement, as LIS professionals, you have to be acquainted with the areas of LIS that are susceptible for mathematical modelling using OR. Studying this book is also recommended to librarians because there is not any other text on information field with the approach the present work has adopted. The previous works mainly consider application of a technique from the OR (eg: transportation) in a library operation (eg: library management).