THE central theme of this special issue is the difference between the way in which we ought to make decisions and how we actually do make them. The area is behavioural decision research (BDR), conducted via a range of methodologies and by many different types of psychologist. Is decision making guided by evolutionary pressures? Why are lotteries so popular? How is our judgement affected by others, for example in a jury? Do we make decisions calmly and rationally, based on all the available evidence? Or are we irrational and impulsive?