MERMAID is a marine scientific instrument platform, short for Mobile Earthquake Recorder for Marine Areas by Independent Divers. MERMAID evolved from a first prototype, developed and built by the Scripps Institution of Oceanography in partnership with Princeton University, to a second, built by Teledyne Webb Research in collaboration with the University of Nice Sophia Antipolis, and now third-generation model, operational today, commercialized by OSEAN SAS in Le Pradet, France. Fourth-generation models add hydrographic monitoring capability to complement the acoustic sensor suite, and are designed to carry out measurement profiles to depths exceeding 4,000 m.