For a long time, economists have assumed that we were cold, self-centred, rational decision makers - so-called Homo economicus; the last few decades have shattered this view. The world we live in and the situations we face are of course rich and complex, revealing puzzling aspects of our behaviour. Optimally Irrational argues that our improved understanding of human behaviour shows that apparent 'biases' are good solutions to practical problems - that many of the 'flaws' identified by behavioural economics are actually adaptive solutions. Page delivers an ambitious overview of the literature in behavioural economics and, through the exposition of these flaws and their meaning, presents a sort of unified theory of behaviouralism, cognitive psychology and evolutionary biology. He gathers theoretical and empirical evidence about the causes of behavioural 'biases' and proposes a big picture of what the discipline means for economics.