The aim of intensity modulated radiation therapy (IMRT) is to kill tumor cells while at the same time protecting the surrounding tissue and organs from the damaging effect of radiation. Given the number of beams and beam directions, beam intensity optimization needs to determine beam intensity profiles that yield the best dose distribution under consideration of clinical and physical constraints. In this book, we first review existing mathematical models and computation methods for the beam intensity optimization problem. Then we formulate the beam intensity optimization problem as a multiobjective linear programme (MOLP) with three objectives. The rest of the book is dedicated to developing methods to solve this large MOLP efficiently and to the application in the beam intensity optimization problem. The book provides the necessary mathmatical foundation of multiobjective optimization to solve multiobjective linear programming problems. It is well suitable to be used as a reference book on multiobjective optimization. Moreover it should also be useful to professionals who may be considering using multiobjective optimization.