The recent advances in mobile and ubiquitous computing, and the development of inexpensive, portable devices are extending the application fields of ad hoc networking far beyond the traditional view of stand-alone networks. Indeed, it is now recognized that a prerequisite for the commercial penetration of the ad hoc networking technologies is an easy access to the Internet and its services, and their integration into traditional wired/wireless infrastructure-based networks. In this chapter we review the different approaches that have been proposed to provide Internet connectivity for ad hoc networks, pointing out advantages and drawbacks of each of them. Possible strategies are to implement an extended Mobile IP Foreign Agent (MIP-FA) or a Network Address Translation (NAT) in the gateway interconnecting the ad hoc network with the external Internet. However, these solutions are based on complex IP-based mechanisms originally designed for the wired Internet. In this chapter we also describe an alternative approach, in which basic layer-2 functionalities are exploited to build a multi-hop heterogeneous (i.e., using wireless and wired links) proactive ad hoc network that could be used as a flexible and low-cost extension of traditional wired LANs. This architecture is validated by an implementation based on the OLSR protocol developed in the framework of the MobileMAN Project.