Today, it is not uncommon for the inhabitants of major cities to have a large selection of network technologies, both wired and wireless, at their fingertips. Hence, to have an unprecedented number of services readily accessible. Whereas the availability of wired technologies is limited to one at a time (e.g., an office LAN, a residential xDSL), as far as wireless technologies are concerned, people are usually exposed to several of them simultaneously (e.g., GSM/GPRS and UMTS cellular networks, WiFi, Bluetooth). Although users commonly rely on one technology at a time for a specific service, considerable research effort has been devoted to inter-operability among technologies, with the aim of granting more band- width to users and, potentially, lower fees. Among recently-developed mobile applications (e.g., the Google Mobile suite, the Traffic Message Channel or the Intermodal Journey Planner), a widespread interest is surrounding those that enable the collection and sharing of various information contents for users on the move. The growth of such services will foster the creation of "virtual communities" of users sharing similar interests and goals: as way of example, students on a campus who share class material, tourists browsing through local attractions listings, car drivers seeking and exchanging traffic information, or pedestrians accessing their domestic or working environment via hand-held devices. Taking into account the previous remarks, it is clear that a fundamental problem in wireless networks is the discovery and sharing of information among users, which can relay on more than one communication technology. While in the context of wired networks, many algorithms and protocols have been presented for content discovery, much fewer proposals target heterogeneous wireless environments. In this chapter, we first review some of the most relevant solutions presented for content discovery, in both wired and wireless contexts (Sections 1.2 and 1.3). We focus on the well-known publish/subscribe asynchronous messaging paradigm and discuss the benefits of designing an overlay network relying on an underlay wireless network. We then introduce a possible network architecture, composed on the one hand of infrastructured nodes, such as WLAN access points and cellular system base stations, and on the other hand of mobile nodes that are equipped with multi-interface wireless terminals, namely, pedestrian users as well as vehicles (Section 1.4). We devise how an overlay network can be created and efficiently implemented on such a communication network using the publish/subscribe paradigm and its content-based routing algorithms. We describe the semantics and the interaction among the logical network entities as well as the possible interface selection strategies (Section 1.5). Finally, we take a heterogeneous wireless networks, including the IEEE 802.11 technology and the UMTS cellular network as a case study, and we show some performance results of the publish/subscribe approach in such a scenario (Sections 1.6 and 1.7).