Abstarct: Aabstract In this thesis, at first we introduce the basic concepts and preliminaries. Also, we express the concepts of (weak, proper) efficiency for multiobjective optimization problem. We deal with the solving of multiobjective optimization problems by applying scalariztion methods. A scalariztion method is a process that consists in replacing the multiobjective optimization problem with an appropriate scalar optimization problem, which is a real-valued optimization problem. We recall some of the scalarization approaches that are related to our proposed methods. In this thesis, some new scalariztion techniques are introduced and the relationships between optimal solutions of these problems and (properly, weakly) efficient solutions of a multi-objective optimization problem are analyzed. In fact, some necessary and sufficient conditions for (proper, weak) efficiency are provided. Thereafter, we analyze a modification of approximate proper efficiency for problems with infinitely many objective functions. We obtain some necessary and sufficient optimality conditions for this modification of approximate proper efficiency. Finally, we investigate efficient solutions of optimization problems with multiple criteria and bounded trade-offs.