Abstract: This invention concerns computer system and method for rating agents participating in electronic transactions. In particular, the invention provides a computer system for rating agents participating in electronic transactions, the system comprising a data store to store a set of rules to describe expected behaviours of a first agent for interactions that take place during an electronic transaction with a second agent, wherein at least one rule describes the expected behaviours in terms of a primary expected behaviour and at least one alternative expected behaviour. The system also comprises a monitoring engine operable to monitor actual behaviours of the first agent for interactions that place during the electronic transaction; and a compliance engine operable to calculate a degree of compliance between the monitored actual behaviours and the expected behaviours.