A bond is simply a promise to pay you certain amounts of money at specific future dates—regular coupon payments and the full face value when the bond matures. The fair price today is what those future payments are worth right now, after we adjust them for the interest rates tied to how far away they are. When those interest rates move, bond prices move, and a big part of investing in bonds is measuring exactly how much. This chapter teaches you how to price a bond from scratch, make sense of different yield numbers, and measure how much a bond’s price swings when interest rates change.