When you purchase a bond, you have several options when it comes to making the most of the investment. If you hold the bond, you can expect to receive regular payments from the bond issuer -- so long as you don't default -- and redeem the bond when it reaches maturity. However, in most cases, you will also have the option of selling the bond before it reaches maturity.
When a bond is issued, it has a certain "life." When the bond matures, you can turn it in to the bond issuer and the issuer will provide the face value of the bond. The bond issuer is contractually obligated to provide this money. However, you may not wish to hold onto the bond for multiple years, but instead sell it before maturity, which is entirely legal.
Selling a Bond
Bonds can be bought and sold on the bond market, just like stocks. Depending on changes in the financial status of the issuer and changes in the interest rate, you may be able to get more or less money for the bond than you bought it for. However, you will need a broker to do this, and a broker will likely charge a commission or another fee for selling the bond.
Changes in Value
The value of the bond will likely have changed since the time it was issued, as bond prices fluctuate constantly. This is because interest rates change regularly. So, if the interest rate falls relative to when the bond was issued, the bond is more valuable by comparison. However, if the interest rate rises, the bond is not worth as much. The creditworthiness of the bond will also affect its value.
The only time that a bond cannot be sold is when there is no demand for it. While most bondholders are able to find a buyer at some price, there are occasions on which a bond is entirely unsaleable, as no one wants to buy it. This bond could be considered illiquid. This may happen when the bond issuer is expected to default on the bond payment.