The control of crack propagation and fracture toughness is essential for lifespan of the components in the field of aerospace. The fracture toughness of Inconel 718 has become important as a design criterion to make safer. This research investigates various influencing factor of Inconel 718 and shows their properties in relation to fracture toughness. To determine the research assignment data were collected and evaluated and metallographic and SEM-examinations were performed. Influencing factors like the primary material, the anisotropy, the grain size or the forging temperature for the fracture toughness are shown and discussed in this master thesis. Generally speaking, the collected data shows a strong variation of the fracture toughness. As a result, it is found that the primary material for the components, the anisotropy of the samples and the structure were the most important factors for the fracture toughness. Other factors of research were the grain size, the Nb-content, the δ-phase, the temperature of the heat treatment, the forging temperature and the mechanical properties. Thereby the grain size shows an insignificant impact on the fracture toughness. In addition, increased forging temperature increase the strength values and reduces the elongation values. However, the fracture toughness remains in the same range of values. Microscope examinations show the δ-phase and the carbides of the material. From the SEM- and the XRD-investigation it can be seen that the fracture is caused by particles, which are niobium carbides and titanium nitrides and their numbers influence the fracture toughness. In conclusion, the researched results are summarized in an influence matrix, which indicates influential and non-influential factors. The most critical factor here is the microstructure, since it as a high active and a high passive sum. From a current state of research, further investigations concerning the carbide and their distribution in the primary material are aimed and they should be integrated in a predictive model for the fracture toughness.