The role of psychology in investment decisions has been amply debated during the past few decades, following the evolution of behavioural finance. This book shows that, although behavioural finance concepts were coined/systemised since the 1980s, their first traces are identified in Joseph de la Vega’s Confusion of Confusions, written in 1688, over 300 years ago. To that end, the book provides the first comprehensive assessment of Confusion of Confusions from the perspective of the behavioural finance paradigm. Offering also a detailed discussion of behavioural finance itself and the historical context of Vega and his time, it demonstrates that Confusion of Confusions constitutes the precursor to behavioural finance. This book should be of interest to finance researchers and students, particularly those focusing on behavioural finance and financial history. The book’s educational value for investors further renders it relevant to regulators and policy makers, who can consider including it in financial education curricula.