This paper focuses on general considerations and ideas on a Maritime Situational Awareness (MSA) system concept addressing specifically the surveillance of the Mediterranean Sea. It presents analysis of the main potentials and limits of existing Maritime Surveillance Systems (MSSs) operating on the Mediterranean Sea and identified technology gaps. The authors then propose MSA system architecture, applications, requirements and sensors. The paper concludes with a few considerations on signal processing and data fusion techniques, required for the implementation of the MSA system capabilities.