We examine the concept of entanglements and the associated entanglement lengths in polymer interfaces. Explicitly, we consider the influence of the compositional inhomogeneity and the manner in which it influences the entanglement lengths. We address this issue by adapting the, packing model of entanglements proposed by Kavassalis and Noolandi. The effects of the compositional inhomogeneity are incorporated through a combination of Monte Carlo simulations and self-consistent-field theory computations. Our results mainly focus on the inhomogeneous variations of entanglements in the interfacial region of polymer blends. In this context, we elaborate upon the connections between our results and the experimentally measurable macroscopic properties like the slip, rheology, and the toughness of polymer-polymer interfaces.