Graph depicting the relation of interest rates to time: time is plotted on the x-axis, and yields on the y-axis. The curve shows whether short-term interest rates are higher or lower than long-term rates. A positive yield curve results if short-term rates are lower, and a negative yield curve results if short-term rates are higher. A flat yield curve results if long- and short-term rates do not differ greatly. Generally, the yield curve is positive because investors tie up their money for longer periods and are rewarded with better yields.