His PhD was a seminal work that introduced the first formalisation of the concept of 'Computational Trust' and applied it to Multi-Agent Systems. It brought together disparate disciplines and attempted to make sense of a vital phenomenon in human and artificial societies, and is still widely referenced today, being in the top tenth of one percent of Citeseerx's most cited articles in computer science. Dr. Marsh's current work builds extensively on this model, applying it to network security, Critical Infrastructure Protection, and mobile device security.