We develop adaptive algorithms and protocols for Cognitive Radio Networks (CRNs). Particularly, we focus on Opportunistic Spectrum Access (OSA) techniques and optimal, integrated, cross-layer protocol designs for Cognitive Radio Ad-Hoc Networks (CRAHNs) and Wireless Sensor Networks (WSNs). As a subsystem of the cognitive radio paradigm, we consider the Wireless Spectrum Sensor Network (WSSN). Such network, not nececessarily physically separated from the CRN, provides the necessary support to perform the cooperative sensing operations which enable the implementation of the OSA approach. Our work jointly addresses the design of CRN protocols and of the WSSN signalling protocols. Within this activity we have developed a flexible simulation framework based on NS2 Miracle. Our framework takes into account physical layer aspects, such as the use of multiple frequencies and the simulation of fading effects, that are not accurately modelled by most of the existing network simulators. Our target applications include CRAHNs coexisting with traditional cellular networks operating on licensed bands as well as sensor networks coexisting with WLANs in unlicensed bands. This activity has been partially funded by the 7th Framework Programme european project ICT-SENDORA.