The motivation behind this examination is to present the theoretical structure of Modeling Activities, which is believed to be a vital device for mathematics instruction. Modeling activities are defined as activities to figure out complex problems faced in real life situations that require the creation of a mathematical model as a product. In order to introduce the modeling activities within the scope of the study, the process of the developments of these activities is given in historical sequences and how they are defined by different educationists in the literature. Different steps of mathematical model formation, principles of mathematical model are illustrated. The importance of modeling activities in mathematics teaching, its different components and how they should be applied in courses are also included.