"How do mental errors or cognitive biases undermine good decision making?" This is the question Steve A. Yetiv takes up in his latest foreign policy study, National Security through a Cockeyed Lens. Yetiv draws on four decades of psychological, historical, and political science research on cognitive biases to illuminate some of the key pitfalls in our leaders' decision-making processes and some of the mental errors we make in perceiving ourselves and the world. Tracing five U.S. national security episodes - the 1979 Soviet invasion and occupation of Afghanistan; the Iran-Contra affair during the Reagan administration; the rise of al-Qaeda, leading to the 9/11 attacks; the 2003 U.S. invasion of Iraq; and the development of U.S. energy policy - Yetiv reveals how a dozen cognitive biases have been more influential in impacting U.S. national security than commonly believed or understood. Identifying a primary bias in each episode-disconnect of perception versus reality, tunnel vision ("focus feature"), distorted perception ("cockeyed lens"), overconfidence, and short-term thinking - Yetiv explains how each bias drove the decision-making process and what the outcomes were for the various actors. His concluding chapter examines a range of debiasing techniques, exploring how they can improve decision making.