Description Development of an advanced multi-robot system for underwater environments Autonomous Underwater Vehicles (AUVs) represent one of the most challenging frontiers for robotics research. AUVs work in an unstructured environment and face unique perception, decision, control and communications difficulties. Currently, the state of the art is dominated by single AUVs limited to open-sea, preplanned trajectories with offline postprocessing of the data gathered during the mission. The use of multiple AUVs as explored in this project is still in a very early research phase. Some of the research issues addressed in this project are even completely uncharted territory, especially the development of functionalities to seamlessly monitor critical underwater infrastructures and detect anomalous situations (e.g., missions related to harbour safety and security) and, also, the study of advanced AUVs capable of interacting with humans to perform such functions as companion/support platforms during scientific and commercial dives. The aim of the Co3-AUVs project is to develop, implement and test advanced cognitive systems for coordination and cooperative control of multiple AUVs. Several aspects will be investigated including 3D perception and mapping, cooperative situation awareness, deliberation and navigation as well as behavioral control strictly linked with the underwater communication challenges. As a result, the team of AUVs will cooperate in challenging scenarios in the execution of missions where all data is processed online. In doing so, the team will be robust with respect to failures and environmental changes. These key features will be tested in a harbour scenario, where additional difficulties arise, compared to open sea applications and in a human diver assistance scenario that also illustrates human robot interaction issues.