Systems, methods, and instrumentalities may implement service-based discovery in a network, such as a 3GPP or 3GPP2 network. A Discovery Server may be used to query and find services offered by the network or by entities that interface with the network. Situational context information or policy information, or both, may be communicated to the discovery server so that the Discovery Server can provide context-aware and policy-based discovery services. The Discovery Server may be used to control which of the entities that interface with the network can discover one another. The Discovery Server may support queries based on, for example, the type of MTC entity, the type of services hosted on the entity, the availability times of the entity, types of protocols supported, levels of Quality of Service (QoS) supported, and MTC-IWF services.