— We propose a physical-datalink cross-layer resource allocation scheme over wireless relay networks for quality-ofservice (QoS) guarantees. By integrating information theory with the concept of effective capacity, our proposed scheme aims at maximizing the relay network throughput subject to a given delay QoS constraint. This delay constraint is characterized by the socalled QoS exponent θ, which is the only requested information exchanged between the physical layer and the datalink layer in our cross-layer design based scheme. Over both amplify-andforward (AF) and decode-and-forward (DF) relay networks, we develop the associated dynamic resource allocation algorithms for wireless multimedia communications. Over DF relay network, we also study a fixed power allocation scheme to provide QoS guarantees. The simulations and numerical results verify that our proposed cross-layer resource allocation can efficiently support diverse QoS requirements over wireless relay networks. Both AF...