If you invest in stocks, you should also be investing in bonds. Bonds provide a measure of certainty (regular income, preservation of principal) that stocks don't have.
However, bonds have some risks associated with them also. If interest rates rise after you have bought a bond, you may be stuck with earning less than the current market rate.
You can trade your lower-interest bond on the open market (for the most part), but you will have to lower the price (loss of principal) to do so.
When interest rates are very low, there is but one way they can move and that is up. When rates will change cannot be anticipated exactly. For example, Japan had record low interest rates for more than a decade.
That's not helpful to investors who want to buy bonds when U.S. interest rates are low, but is does illustrate that while interest rates seldom remain low or high for extended periods, it is possible.
When interest rates look like the only way they can go is up, investors may want to consider two types of U.S. Treasury issues that adjust their interest rates with inflation. Rising interest rates generally mean the economy is growing and there will be some growth in inflation.
The TIPS and I Series Treasury issues address the problem of owning a bond and earning a higher interest rate when inflation and interest rates rise.
The Treasury Department provides a good side by side comparison of the two bonds. Investors looking for protection against future interest rate increases should consider these two options.