This chapter has two main goals: to provide a brief history of military spending globally and in the U.S. specifically, and to introduce the major questions considered in this book. Global military spending in 2017 was $1.74 trillion, 73 percent of which was accounted for by the 10 highest-spending countries, led by the U.S. In fact, the U.S.’s military expenditure is nearly three times that of the second-highest spender, China, and larger than the next nine biggest military spenders combined. Such high spending has both substantial direct and indirect effects on the economy. Although an ever-growing literature has examined the effect of military spending on economic growth, there have been very few studies analysing its impact on profitability. This book aims to fill this gap. In addition to exploring general questions like how military spending affects economic growth and the role of military spending in capitalism according to Marxist thought, the book primarily investigates how military spending affects the rate of profit and whether this effect changes with respect to the development level of each country’s economy or its role in the arms trade.