One of the main issues of concern regarding the quality control of Inconel alloys is the precipitation of δ-phase, which in certain quantities and morphologies can lead to a loss in fracture toughness; it is therefore important to be able to properly detect and quantify it. X-ray diffraction (XRD) is a well-established and widely used technique for qualitative and quantitative analysis; however, the quality of its results depends on prior knowledge of the exact structure of each phase. The information on δ-phase available in the literature is incomplete and several discrepancies exist among different publications; furthermore, doubts persist regarding the interaction of δ and γ’’ phases. The aim of this work is to evaluate the structure of δ-phase in Inconel 718 alloys. This was achieved through a combination of experimental results, obtained for samples of the alloy that were subjected to three different heat treatments in order to produce different concentrations of δ-phase, and comparison of these with simulated results. This methodology allowed a global view of the mechanics of phase transformations in the alloy and to the correct identification of diffraction lines for δ-phase.