The problem of setting a revised target for the side batting second when a game of one day cricket has been interrupted by the weather is one that has baffled the world's cricket authorities for more than 30 years. This paper describes how a fair method was devised based on a mathematical model of the run scoring process during an innings, and how this has led to the development of the ‘Duckworth/Lewis’ method which is now used in most parts of the world where cricket is played.