This chapter presents experimental and theoretical issues related to the cooperative path-following of unmanned marine vehicles (UMVs) focusing on the application of vehicle-following and methodological aspects regarding the design of suitable metrics for performance evaluation of the proposed guidance techniques. Unmanned surface vehicles (USVs), thanks to their position at the air-sea interface, can play a key role in the networks of heterogeneous manned/unmanned air, ground and marine platforms that characterize the next-century scenarios of environmental monitoring, border surveillance, warfare and defence applications. Indeed, they can act as communication nodes connecting radio frequency networks in air and acoustic ones undersea, monitoring ocean and atmosphere dynamics as well as surface and underwater intrusions. In particular, USVs are naturally seen as a part of flotillas of heterogeneous vehicles executing large-scale surveys and supporting rapid environmental assessment (REA), and an increasing number of prototype vehicles have been developed for science, bathymetric mapping, defence and general robotics research.