Do governments support their own bonds when their value goes down?
Companies do not support their stock. Once the security is out on the wild (market), its price fluctuates according to what investors think they are worth. Support is a whole different concept, financially speaking: Support or support level refers to the price level below which, historically, a stock has had difficulty falling. It is the level at which buyers tend to enter the stock. So it is the lowest assumed price for that stock. Once it reaches its price, buyers will rush to the stock, raising its price. The company wants to keep the stock price at acceptable levels, as it can be seen as the general view of the company's health. Also several employees/executives in the company have stock or stock options, so it is in their interest to keep their stock price up. A bond that goes down in value may indicate a believe the bond issuer (government in this case) won't honor the bond when it matures. As for bonds, there is a wealth of reading in this site: Can someone explain how government bonds work? Who sets the prices on government bonds?  Basic understanding of bonds, values, rates and yields