Chemical composition and significance of the interfaces in Cr/Be layered structures depending on the thickness and ordering of beryllium and chromium layers were considered in details. Absence of pure Be and Cr layers and the formation of two beryllides, CrBe ₁₂ and CrBe ₂, depending on the order of layer deposition was established in the systems with layer thickness less than 2.0 nm. This fact indicates a strong layer intermixing and is explained by both the ballistic layer intermixing and surface-free energy minimization processes. Insertion of an ultrathin barrier layer (Si, C, B ₄C) between the ultrathin base layers simultaneously affects the formation of both interfaces. In the case of such ultrathin multilayer systems, the task of specific interface engineering by a barrier layer insertion appears to become much more complicated due to the strong layer intermixing occurring through the deposition process and further diffusion. Both interfaces are inseparable and a chemical change in one inevitably causes a chemical change in the second.