In emergencies or disasters a key support factor for situation awareness, decision making and response is to provide a secure and dependable network infrastructure that aggregates connectivity over all available heterogeneous wireless broadband access technologies, including those employed for commercial network access, which adapts to mission critical application requirements and enables immediate and robust communications among command centres, rescue workers and affected population. This dissertation is aiming at a secure by design, distributed, open, self-configured and emergency-aware network and service architecture for automated, secure and dependable support of multiple mission critical applications in highly demanding and dynamic emergency environments. This thesis proposes and develops a secure and dependable overlay network model that hides heterogeneity of the underlying networks and support the multiplicity of communication needs across different types of users and user groups in emergencies. It also designs and implements an integrated comprehensive security architecture that combines pro active and reactive security mechanisms, taking into account cross-layer considerations and multi-operator emergency environments. In terms of pro active security, the dissertation introduces a family of key agreement methods based on weak to strong authentication associated with several multiparty contributory key agreement schemes. In the area of reactive security, the dissertation introduces anomaly-based wireless intrusion detection algorithms for the detection of various attacks on the wireless channels. Finally, it includes prototype implementation of the reactive security algorithms and proof of concept evaluation and validation of the proposed emergency response architecture and the developed security mechanisms through a series of experiments at local and metropolitan scale test-beds.