Originally published in 1988, the purpose of this title was to present a coherent summary of the previous 30 years’ of research on the way in which animals and humans distribute their behaviour between alternative sources of reinforcement. There were three reasons why the book was needed at the time. First, it makes use of the empirical results available, something only partially present in many theories of the time. Second, as a general source of information to gain understanding of the scope of research on behaviour allocation. Third, a text was needed that described the techniques of experimental design and data analysis in this area.