Abstract: The objective of this research was to examine the competitive structure of the international tourist market, to establish how and with whom destinations compete. Instead of adopting traditional perceptual methods for identifying and describing competitors, this thesis takes an empirical approach by applying the behaviourally grounded Duplication of Purchase Law.The Duplication of Purchase (DOP) Law is an empirical generalisation that illustrates the structure of competitive markets through simple patterns of repeat purchase (Goodhardt, Ehrenberg et al. 1984). It states that brands share their customers with other brands in line with penetration levels, where penetration is the proportion of people who buy an item at all in any given time period (Uncles, Ehrenberg et al. 1995; Ehrenberg, Uncles et al. 2003). This means that any brand will share customers more with other bigger brands and far less with the smaller brands. Consequently, it is a very useful tool that can help identify and predict the competitive market structure, by simply knowing each individual brand's market share.This research specifically addresses whether the DOP Law can be successfully applied to the international tourist market using destinations as brands. It analyses and predicts how brands such as 'Destination France' or Destination USA' compete on an international scale, and discusses the instances where the competition is identified as being substantially more, or less, intense. Such exceptions to the DOP Law are often referred to as 'partitions'.