For some researchers - particularly those working in AI - the term `agent' has a stronger and more specific meaning than that sketched out above. These researchers generally mean an agent to be a computer system that, in addition to having the properties identified above, is either conceptualised or implemented using concepts that are more usually applied to humans. For example, it is quite common in AI to characterise an agent using mentalistic notions, such as knowledge, belief, intention, and obligation [Shoham, 1993]. Some AI researchers have gone further, and considered emotional agents [Bates, 1994][Bates et al., 1992a]. (Lest the reader suppose that this is just pointless anthropomorphism, it should be noted that there are good arguments in favour of designing and building agents in terms of human-like mental states - see section 2.) Another way of giving agents human-like attributes is to represent them visually, perhaps by using a cartoon-like graphical icon or an animated face [Maes, 1994a] - for obvious reasons, such agents are of particular importance to those interested in human-computer interfaces.