Wireless Sensor Networks (WSNs) have been slowly moving into the mainstream as remote monitoring solutions – especially in hostile, hard-to-reach or otherwise complicated scenarios, where deployment of a traditional network may be unpractical. Some of the envisioned applications, such as wildlife monitoring, introduce an additional difficulty by featuring mobile elements. In these circumstances traditional routing techniques must be abandoned in favour of Opportunistic Routing (OR), which uses mobility to its advantage by having nodes carry around messages. This dissertation addresses the issue of Opportunistic Routing in WSNs. An overview of existing solutions is presented, followed by the description of a new Convergent Hybrid-replication Approach to Routing in Opportunistic Networks (CHARON). This approach is focused on simplicity and efficiency, aiming for real-world applicability. It primarily routes messages based on estimated delay, and supports basic Quality of Service (QoS) mechanisms. It also provides built-in radio power management, a seldom found feature. A reference implementation of CHARON is then presented, accompanied by simulation and real-world test results that show this solution is capable of achieving good delivery statistics with high efficiency.