Is it a good idea to invest in bonds?

A bond is a debt investment in which you as an investor loan money to an entity (typically corporate or governmental) for a defined period of time at a variable or fixed interest rate. It all depends on which bonds you purchase and at what price. Bonds can be a good addition to your portfolio to keep it well diversified. If you are unsure, I would recommend talking to a qualified planner to help you decide on the right allocation.

The upside of a bond is you get your money back with interest.  When interest rates go down you can make addition gains intra-maturity due the mathmatics of bond investing.  With interest rates low you need to be more careful about what types of bonds you invest in.  I would look for cushion bonds.  You can learn more here:   http://seekingalpha.com/article/1358261-protect-your-portfolio-with-cushion-bonds

I would be careful of bond ETFs and mutual funds because they don't have a fixed maturity - that is you never get your money back.  This makes them much more risky.

If you're serious, I would find an advisor that understands the bond market and invests in individual bond issues not etfs and mutual funds.

Bonds would be one method of investing if you are looking for income. Among the negatives in bond investing currently are the spectre of rising interest rates which can/will cause a loss in the value of bonds and the inability of non-institutional buyers to get a good price when buying or selling bonds. The price quoted by bond dealers varies widely depending on how many bonds you want to buy or sell. If you are investing less than $100,000 in bonds, you are better off in fixed income Exchange Traded Funds (ETF's) both from a diversification standpoint and from the ability to pick maturities to protect against rate increase risk. Over $100,000, you can and should hire a professional fixed income manager to construct a portfolio for you.