Reference systems are essential for navigation and surveying as well as for determining the shape of the Earth and its position and orientation in space. They are required for the precise determination of satellite orbits and serve as basis for Earth science applications such as measurements of the Earth's gravity field, atmosphere studies, detection of plate tectonic motion or global sea level change monitoring. The International Terrestrial Reference Frame is the realization of the International Terrestrial Reference System. It is generated by combining observational data of the space geodetic techniques Global Navigation and Satellite Systems, Very Long Baseline Interferometry, Satellite Laser Ranging and Doppler Orbitography and Radiopositioning Integrated by Satellite. The purpose of combining the techniques is to exploit their individual strengths, since each technique is characterized by varying potential when it comes to determining certain geodetic parameters. The combination centers of the International Earth Rotation and Reference Systems Service are responsible for the creation of the ITRF. They apply different strategies for the combination of the data. Comparisons of the independent solutions improve the reliability and provide an assessment of the accuracy of the ITRF. In this thesis the similarities and differences of the two approaches are discussed. Furthermore, based on the VLBI campaign CONT14, both methods are compared by estimating coordinates of the participating stations. Thereby the results of the combination of solutions depend more on arbitrary operator decisions. However, when identical conditions are applied to define the geodetic datum, the resulting station coordinates only differ on the sub-millimeter level.