This paper describes the problem of ambush marketing: the act of attempting to associate with an event without buying the rights to do so. From the perspective of the organizers and sponsors of large-scale media and athletic events, the problem is significant. More than $100 billion is spent annually on purchasing sponsorship rights and the associated promotions. For companies who have not paid for such rights to be able to imply an association with these high-profile events dilutes the value of that sponsorship. Despite the size of the problem, however, (and except for the special coverage many countries afford Olympic activities) there is little legal protection against all but the most blatant marketing encroachment.