The reason why the author has chosen the problem of adhesion of multi-component injection molding parts in this research work is that there is still a wide disagreement on what exactly are the decisive procedures in the process of the appearance of adhesion. Thus, the motivation aroused to determine significant process parameters which influence the bond strength, as well as the driving forces behind the processes that take place during the formation of a multi-component plastic part. To attain this goal, an injection mold was developed to produce several different two-shot molded test specimens. The geometry of these test specimens was constructed to simulate different stress conditions into the contact area by the usage of a standard tensile testing machine. By the usage of factorial designs and a mathematical software, it became possible to identify the melt temperature of the second component as the most significant process parameter for the bond strength. A detailed examination of this process parameter leads to the conclusion that a successive increase of the melt temperature of the second component is directly connected to a steady increase in the bond strength, if the first component is an amorphous thermoplastic. If, however, the first component is made of semi-crystalline thermoplastic polymers, a successive increase of the melt temperature of the second component leads to a sudden steep increase in the bond strength. A well-known dilemma during the production of multi-component plastic parts is the usage of color masterbatches. These masterbatches can minimize the adhesion between the components to a level where these multi-component plastic parts cannot be used in their original intended application. In this work this phenomenon was considered and a reversion of this effect was achieved. In order to find out the driving forces behind the formation of adhesion, Raman-spectroscopic investigations at the contact areas of the bonded parts were carried out. On the basis of these results it was possible to identify existing mixed spectra in the area of contact. These mixed spectra are clear evidence for the existence of interdiffusion processes between the two materials across the contact area. Moreover, a direct relationship between the melt temperature of the second component, the bond strength size and the diffusion zone's length could be determined. All findings in this work show diffusion as the most decisive process that takes place during the formation of adhesion in the multi-component injection molding.