What traditionally happens to bonds when the stock market crashes?
The short answer is if you own a representative index of global bonds (say AGG) and global stocks (say ACWI) the bonds will generally only suffer minimally in even the medium large market crashes you describe.  However, there are some caveats. Not all bonds will tend to react the same way.  Bonds that are considered higher-yield (say BBB rated and below) tend to drop significantly in stock market crashes though not as much as stock markets themselves.  Emerging market bonds can drop even more as weaker foreign currencies can drop in global crashes as well. Also, if a local market crash is caused by rampant inflation as in the US during the 70s-80s, bonds can crash at the same time as markets.  There hasn't been a global crash caused by inflation after countries left the gold standard, but that doesn't mean it can't happen. Still, I don't mean to scare you away from adding bond exposure to a stock portfolio as bonds tend to have low correlations with stocks and significant returns.  Just be aware that these correlations can change over time (sometimes quickly) and depend on which stocks/bonds you invest in. It depends.  Very generally when yields go up stocks go down and when yields go down stocks go up (as has been happening lately). If we look at the yield of the 10 year bond it reflects future expectations for interest rates.  If the rate today is very low but expectations are that the short term rates will go up that would be reflected in a higher yield simply because no one would buy the longer term bond if they could simply wait out and get a better return on shoter term investments.  If expectations are that the rate is going down you get what's called an inverted yield curve.  The inverted yield curve is usually a sign of economic trouble ahead.  Yields are also influenced by inflation expectations as @rhaskett is alluding in his answer. So.  If the stock market crashes because the economy is doing poorly and if interest rates are relatively high then people would expect the rates to go down and therefore bonds will go up! However, if there's rampant inflation and the rates are going up we can expect stocks and bonds to move in opposite directions.  Another interpretation of that is that one would expect stock prices to track inflation pretty well because company revenue is going to go up with inflation.  If we're just talking about a bump in the road correction in a healthy economy I wouldn't expect that to have much of an immediate effect though bonds might go down a little bit in the short term but possibly even more in the long term as interest rates eventually head higher.  Another scenario is a very low interest rate environment (as today) with a stock market crash and not a lot of room for yields to go further down. Both stocks and bonds are influenced by current interest rates, interest rate expectations, current inflation, inflation expectations and stock price expectation.  Add noise and stir. It depends on why the stocks crashed. If this happened because interest rates shot up, bonds will suffer also. On the other hand, stocks could be crashing because economic growth (and hence earnings) are disappointing. This pulls down interest rates and lifts bonds.
The price of a bond goes up when yields go down.  For example, you purchase a 5% bond today for $100 and the very next day the same bond is being offered with a rate of 10%.  Will you be able to sell you bond for the $100 you paid?  No, you must compete with the 10% bonds being sold so you will have to sell your bond for less than the $100 you paid to compete with the new bonds being sold.  Thus, bond prices are inversely related to bond yields. The 20-year index you cited tracks bond prices and bond prices have gone up over the last 10 years which means bond yields have gone down.  Why have bond prices gone up?  Demand.  More investors are moving their savings into bonds.  Why?  I believe there a couple of reasons.  One, US Treasuries are thought to be one of the safest investments.  With the financial crisis and increased stock market volatility (see chart below) more investors are allocating more of their portfolios to safer investments.  Two, a large portion of the US population is approaching retirement (see chart below).  These folks are not interested in watching their retirement portfolios potentially shrink in the stock market so they move into bonds. The only purpose the ILS market fills is directly lining up capital to pay for potential cats. Unless you're doing directly that you don't really have a way to participate, long or short.  The cat bond market really isn't liquid or developed enough for derivatives to exist at this point.   Due to the losses this year the cat bond market could shrink significantly too because all the existing catastrophe models have seemed to be inadequate to model these occurrences and investors are losing their shirts. There are questions of the extent to which the alternative capital in the reinsurance market will reload in the wake of 2017. When the market moves significantly, you should rebalance your investments to maintain the diversification ratios you have selected. That means if bonds go up and stocks go down, you sell bonds and buy stocks (to some degree), and vice versa. Sell high to buy low, and remember that over the long run most things regress to the mean. The only reason I can think of is that the bonds are bought automatically by some investment pools, groups or institutions. That will stop very quickly once the management finds some other place to put the money. When interest rates rise, the price of bonds fall because bonds have a fixed coupon rate, and since the interest rate has risen, the bond's rate is now lower than what you can get on the market, so it's price falls because it's now less valuable. Bonds diversify your portfolio as they are considered safer than stocks and less volatile. However, they also provide less potential for gains. Although diversification is a good idea, for the individual investor it is far too complicated and incurs too much transaction costs, not to mention that rebalancing would have to be done on a regular basis. In your case where you have mutual funds already, it is probably a good idea to keep investing in mutual funds with a theme which you understand the industry's role in the economy today rather than investing in some special bonds which you cannot relate to. The benefit of having a mutual fund is to have a professional manage your money, and that includes diversification as well so that you don't have to do that. If the equity market in the USA crashed, its very likely equity markets everywhere else would crash. The USA has a high number of the world's largest businesses and there are correlations between equity markets. So you need to think of equities as a global asset class, not regional. Your question is then a question about the correlation between equity markets and currency markets.  Here's a guess: If equity markets crashed, you would see a lot of panic selling of stocks denominated in many currencies, but probably the most in USD, due to the large number of the world's largest businesses trading on US stock exchanges. Therefore, when the rest of the world sells US equities they receive cash USD, which they might sell for their local currency. That selling pressure would cause USD to fall. But, when equity markets crash there's a move to safety of the bond markets. The world's largest bond markets are denominated in which currency? Probably USD. So those who receive USD for their equities are going to spend that USD on bonds. In which case there is probably no correlation between equity markets and currency markets at all. A quick google search shows this kind of thing Investopedia has a good explanation of the term shorting which is what this is. In the simplest of terms, someone is borrowing the bond and selling it with the intent to replace the security and any dividends or coupons in the end. The idea is that if a bond is overvalued, one may be able to buy it back later for a cheaper price and pocket the difference. There are various rules about this including margin requirements to maintain since there is the risk of the security going up in price enough that someone may be forced into a buy to cover in the form of a margin call. If one can sell the bond at $960 now and then buy it back later for $952.38 then one could pocket the difference. Part of what you aren't seeing is what are other bonds doing in terms of their prices over time here. The key point here is that brokers may lend out securities and accrue interest on loaned securities for another point here. Those are the expected yields; they are not guaranteed. This was actually the bread and butter of Graham Newman, mispriced bonds.  Graham's writings in the Buffett recommended edition of Securities Analysis are invaluable to bond valuation. The highest yielder now is a private subsidiary of Société Générale.  A lack of financial statements availability and the fact that this is the US derivatives markets subsidiary are probably the cause of the higher rates. The cost is about a million USD to buy them. The rest will be similar cases, but Graham's approach could find a diamond; however, bonds are big ticket items, so one should expect to pay many hundreds of thousands of USD per trade. "In general, yes. If interest rates go higher, then any existing fixed-rate bonds - and hence ETFs holding those bonds - become less valuable. The further each bond is from maturity, the larger the impact. As you suggest, once the bonds do mature, the fund can replace them at a market price, so the effect tails off. The bond market has a concept known as ""duration"" that helps reason about this effect. Roughly, it measures the average time from now to each payout of the bond, weighted by the payout. The longer the duration, the more the price will change for a given change in interest rates. The concept is just an approximation, and there are various slightly different ways of calculating it; but very roughly the price of a bond will reduce by a percentage equal to the duration times the increase in interest rates. So a bond with a duration of 5 years will lose 5% of its value for a 1% rise in interest rates (and of course vice-versa). For your second question, it really depends on what you're trying to achieve by diversifying - this might be best as a different question that gives more detail, as it's not very related to your first question. Short-term bonds are less risky. But both will lose value if the underlying company is in trouble. Gilts (government bonds) are less risky than corporate bonds." While debt increases the likelihood and magnitude of a crash, speculation, excess supply and other market factors can result in crashes without requiring excessive debt. A popular counter example of crashes due to speculation is 16th century Dutch Tulip Mania.  The dot com bubble is a more recent example of a speculative crash. There were debt related issues for some companies and the run ups in stock prices were increased by leveraged traders, but the actual crash was the result of failures of start up companies to produce profits. While all tech stocks fell together, sound companies with products and profits survive today. As for recessions, they are simply periods of time with decreased economic activity. Recessions can be caused by financial crashes, decreased demand following a war, or supply shocks like the oil crisis in the 1970's. In summary, debt is simply a magnifier. It can increase profits just as easily as can increase losses. The real problems with crashes and recessions are often related to unfounded faith in increasing value and unexpected changes in demand. While JB King says some useful things, I think there is another fundamental reason why stock markets go down after disasters, either natural or man-made.  There is a real impact on the markets - in the case of something like 9/11 due to closed airport, higher security costs, closer inspections on trade goods, tighter restrictions on visas, real payments for the rebuilding of destroyed buildings and insurance payouts for killed people, and eventually the cost of a war. But almost as important is the uncertainty and risk. Nobody knew what was going to happen in the days and weeks after an attack like that. Is there going to be another one a week later, or every week for the next year? Will air travel become essentially impractical? Will international trade be severely restricted? All those would have a huge, massive effect on the economy. You may argue that those things are very unlikely, even after something like 9/11. But even a small increase in the likelihood of a catastrophic economic crash is enough to start people selling. There is another thing that drives the market down. Even if most people are sure that there won't be a catastrophic economic crash, they know that other people think there might be and so will sell. That will drive the market down. If they know the market is going down, then sensible traders will start to sell, even if they think there is zero risk of a crash. This makes the effect worse. Eventually prices will drop so far that the people who don't think there is a crash will start to buy, so they can make a profit on the recovery. But that usually doesn't happen until there has been a substantial drop. Because stock markets don't always go up, sometimes they go down. Sometimes they go way down. Between 2007 and 2009 the S&P 500 lost over half its value. So if in 2007 you thought you had just enough to retire on, in 2009 you'd suddenly find you had only half of what you needed! Of course over the next few years, many of the stocks recovered value, but if you had retired in 2008 and depended on a 401k that consisted entirely of stocks, you'd have been forced to sell a bunch of stocks near the bottom of the market to cover your retirement living expenses. Bonds go up and down too, but usually not to the same extent as stocks, and ideally you aren't selling the bonds for your living expenses, just collecting the interest that's due you for the year. Of course, some companies and cities went bankrupt in the 2008 crisis too, and they stopped making interest payments.  Another risk is that you may be forced to retire before you were actually planning to. As you age you are at increasing risk for medical problems that may force an early retirement. Many businesses coped with the 2008 recession by laying off their older workers who were earning higher salaries. It wasn't an easy environment for older workers to find jobs in, so many folks were forced into early retirement. Nothing is risk free, so you need to make an effort to understand what the risks are, and decide which ones you are comfortable with. "You ask two questions - First - the market value can drop for two reasons (that I know), the company itself may have issues, and investors don't trust they'll be paid, or a general rise in interest rates. In the latter case, there's little to worry about, but for the former, well, that's your decision, you say ""the company is in trouble"" yet you believe they'll pay. Tough call. Second - yes, when a bond matures, the money appears in your account." Why does the rising price of a bond pushes it's yield down? The bond price and its yield are linked; if one goes up, the other must go down. This is because the cash flows from the bond are fixed, predetermined. The market price of the bond fluctuates. Now what if people are suddenly willing to pay more for the same fixed payments? It must mean that the return, i.e. the yield, will be lower. Here we see that risk associated with the bonds in question has   skyrocketed, and thus bonds' returns has skyrocketed, too. Am I right? The default risk has increased, yes. Now, I assume that bonds' price is determined by the market (issued by   a state, traded at the market). Is that correct? Correct, as long as you are talking about the market price. Then who determines bonds' yields? I mean, isn't it fixed? Or - in the   FT quote above - they are talking about the yields for the new bonds   issued that particular month? The yield is not fixed - the cash flows are. Yield is the internal rate of return. See my answer above to your first question. Cash would be the better alternative assuming both stocks take a major hit in ALL categories AND the Fed raise rates at the same time for some reason. Money market funds that may have relatively low yields at the moment would likely be one of the few securities not to be repriced downward as interest rates rising would decrease bond values which could be another crash as I could somewhat question how broad of a crash are you talking here. There are more than a few different market segments so that while some parts may get hit really hard in a crash, would you really want to claim everything goes down? Blackrock's graphic shows in 2008 how bonds did the best and only it and cash had positive returns in that year but there is something to be said for how big is a crash: 20%, 50%, 90%?