This chapter discusses the role of speculation in the financial markets that influences individual and group behavior in the form of bubbles and crashes. The chapter highlights behavioral finance issues associated with bubbles, such as overconfidence, herding, group polarization, groupthink effect, representativeness bias, familiarity issues, grandiosity, excitement, and the overreaction and underreaction to prices. These issues are important for understanding past financial mistakes because history often repeat itself. The chapter also examines the aftermath of the financial crisis of 2007–2008 on investor psychology, including the impact of a severe financial downturn, anchoring effect, recency bias, worry, loss averse behavior, status quo bias, and trust. The aftermath of the financial crisis might have negative long-term effects on investor psychology in which some investors remain overly risk averse, resulting in under-investment in stocks and over-investment in cash and bonds.