Are limit orders safe?
I assume you're talking about a sell order, not a buy order. When you place a limit sell order, your order is guaranteed to be placed at that price or higher.  If the market is currently trading much higher than the price of your sell order, then your mistakenly low limit order will be essentially a market order, and will be filled at  the current bid price. So the only way this is a problem is if you want to place a limit sell that is much higher than the current market, but mistakenly place a limit lower than the current market. Limit orders are generally safer than market orders. Market orders take whatever most-favorable price is being offered. This can be especially dangerous in highly volatile stocks which have a significant spread between the bid and ask. That being said, you want to be very careful that you enter the price you intend into a limit order. It is better to be a bit slower at entering your orders than it is to make a terrible mistake like the one you mention in your question.
Not all limit orders add liquidity, but all market orders remove liquidity presuming there is liquidity to remove. A liquidity providing order is one that is posted to the limit book. If an order, even a limit order, is filled before being posted to the limit book, it removes liquidity. Liquidity is measured by a balance and abundance of quantities posted on the limit book and the best spread between the lowest ask and the highest bid. "What you are saying is a very valid concern.  After the flash crash many institutions in the US replaced ""true market orders"" (where tag 40=1 and has no price) with deep in the money limit orders under the hood, after the CFTC-SEC joint advisory commission raised concerns about the use of market orders in the case of large HFT traders, and concerns on the lack of liquidity that caused market orders that found no limit orders to execute on the other side of the trade, driving the prices of blue chip stocks into the pennies.  We also applaud the CFTC requesting comment regarding whether it is   appropriate to restrict large order execution design that results in   disruptive trading. In particular, we believe there are questions   whether it is ever appropriate to permit large order algorithms that   employ unlimited use of market orders or that permit executions at   prices which are a dramatic percentage below the present market price   without a pause for human review So although you still see a market order on the front end, it is transformed to a very aggressive limit in the back end. However, doing this change manually, by selling at price 0 or buying at 9999 may backfire since it may trigger fat finger checks and prevent your order from reaching the market.  For example BATS Exchange  rejects orders that are priced too aggressively and don't comply with the range of valid prices.  If you want your trade to execute right now and you are willing to take slippage in order to get fast execution, sending a market order is still the best alternative." Firstly what are you trading that you could lose more than you put in? If you are simply trading stocks you will not lose more than you put in, unless you are trading on margin. A limit order is basically that, a limit on the maximum price you want your buy order bought at or the minimum price you want your sell order sold at. If you can't be glued to the screen all day when you place a limit order, and the market moves the opposite way, you may miss out on your order being executed. Even if you can be in front of the screen all day, you then have to decide if you want to chase the market of miss out on your purchase or sale. For example, if a stock is trading at $10.10 and you put a limit buy order to buy 1000 shares at or below $10.00 and the price keeps moving up to $10.20, then $10.30 and then $10.50, until it closes the day at $11.00. You then have the choice during the day to miss out on buying the shares or to increase your limit order in order to buy at a higher price. Sometime if the stock is not very liquid, i.e. it does not trade very often and has low volume, the price may hit $10.00 and you may only have part of your order executed, say 500 out of your 1000 shares were bought. This may mean that you may have to increase the price of your remaining order or be happy with only buying 500 shares instead of 1000. The same can happen when you are selling (but in reverse obviously). With market order, however, you are placing a buy order to buy at the next bid price in the depth or a sell order to sell at the next offer price in the depth. See the market depth table below:  Note that this price depth table is taken before market open so it seems that the stock is somewhat illiquid with a large gap between the first and second prices in the buyers (bid) prices. When the market opened this gap is closed, as WBC is a major Australian bank and is quite liquid. (the table is for demonstration purposes only). If we pretend that the market was currently open and saw the current market depth for WBC as above, you could decide to place a limit sell order to sell 1000 shares at say $29.91. You would sell 100 shares straight away but your remaining 900 sell order will remain at the top of the Sellers list. If other Buyers come in at $29.91 you may get your whole sale completed, however, if no other Buyers place orders above $29.80 and other Sellers come into the market with sell orders below $29.91, your remaining order may never be executed. If instead you placed a market sell order you would immediately sell 100 shares at $29.91 and the remaining 900 shares at $29.80. (so you would be $99 or just over 0.3% worse off than if you were able to sell the full 1000 shares at $29.91). The question is how low would you have had to lower your limit order price if the price for WBC kept on falling and you had to sell that day? There are risks with whichever type of order you use. You need to determine what the purpose of your order is. Is it to get in or out of the market as soon as possible with the possibility of giving a little bit back to the market? Or is it to get the price you want no matter how long it takes you? That is you are willing to miss out on buying the shares (can miss out on a good buy if the price keeps rising for weeks or months or even years) or you are willing to miss out on selling them right now and can wait for the price to come back up to the price you were willing to sell at (where you may miss out on selling the shares at a good price and they keep on falling and you give back all your profits and more). Just before the onset of the GFC I sold some shares (which I had bought a few years earlier at $3.40) through a market order for $5.96. It had traded just above $6 a few days earlier, but if instead of a market order I had placed a limit order to sell at $6.00 or more I would have missed out on the sale. The price never went back up  to $6 or above, and the following week it started dropping very quickly. It is now trading at about $1.30 and has never gone back above $2.00 (5.5 years later). So to me placing a limit order in this case was very risky. The obvious thing would happen. 10 shares change owner at the price of $100. A partially still open selling order would remain. Market orders without limits means to buy or sell at the best possible or current price. However, this is not very realistic. Usually there is a spread between the bid and the ask price and the reason is that market makers are acting in between. They would immediately exploit this situation, for example, by placing appropriately limited orders. Orders without limits are not advisable for stocks with low trading activity. Would you buy or sell stuff without caring for the price? "value slip below vs ""equal a bank savings account’s safety"" There is no conflict.  The first author states that money market funds may lose value, precisely due to duration risk.  The second author states that money market funds is as safe as a bank account.  Safety (in the sense of a bond/loan/credit) mostly about default risk. For example, people can say that ""a 30-year U.S. Treasury Bond is safe"" because the United States ""cannot default"" (as said in the Constitution/Amendments) and the S&P/Moody's credit rating is the top/special. Safety is about whether it can default, ex. experience a -100% return.  Safety does not directly imply Riskiness. In the example of T-Bond, it is ultra safe, but it is also ultra risky. The volatility of 30-year T-Bond could be higher than S&P 500.  Back to Money Market Funds.  A Money Market Fund could hold deposits with a dozen of banks, or hold short term investment grade debt. Those instruments are safe as in there is minimal risk of default. But they do carry duration risk, because the average duration of the instrument the fund holds is not 0.  A money market fund must maintain a weighted average maturity (WAM) of 60 days or less and not invest more than 5% in any one issuer, except for government securities and repurchase agreements.  If you have $10,000,000, a Money Market Fund is definitely safer than a savings account.  1 Savings Account at one institution with amount exceeding CDIC/FDIC terms is less safe than a Money Market Fund (which holds instruments issued by 20 different Banks).  Duration Risk Your Savings account doesn't lose money as a result of interest rate change because the rate is set by the bank daily and accumulated daily (though paid monthly).  The pricing of short term bond is based on market expectation of the interest rates in the future. The most likely cause of Money Market Funds losing money is unexpected change in expectation of future interest rates.  The drawdown (max loss) is usually limited in terms of percentage and time through examining historical returns.  The rule of thumb is that if your hold a fund for 6 months, and that fund has a weighted average time to maturity of 6 months, you might lose money during the 6 months, but you are unlikely to lose money at the end of 6 months. This is not a definitive fact.  Using GSY, MINT, and SHV as an example or short duration funds, the maximum loss in the past 3 years is 0.4%, and they always recover to the previous peak within 3 months. GSY had 1.3% per year return, somewhat similar to Savings accounts in the US." A stop-loss order becomes a market order when a trade has occurred at or below the trigger price you set when creating the order. This means that you could possibly end up selling some or all of your position at a price lower than your trigger price. For relatively illiquid securities your order may be split into transactions with several buyers at different prices and you could see a significant drop in price between the first part of the order and the last few shares. To mitigate this, brokers also offer a stop-limit order, where you set not only a trigger price, but also a minimum price that you are will to accept for your shares. This reduces the risk of selling at rock bottom prices, especially if you are selling a very large position. However, in the case of a flash crash where other sellers are driving the price below your limit, that part of your order may never execute and you could end up being stuck with a whole lot of shares that are worth less than both your stop loss trigger and limit price. For securities that are liquid and not very volatile, either option is a pretty safe way to cut your losses. For securities that are illiquid and/or very volatile a stop-limit order will prevent you from cashing out at bottom dollar and giving away a bargain to lurkers hanging out at the bottom of the market, but you may end up stuck with shares you don't want for longer than originally planned. It's up to you to decide which kind of risk you prefer. Yes, you can do this buy placing a conditional order to buy at market if the price moves to 106 or above. Once the price hits 106 your market order will hit the market and you will purchase the stock at 106 or above. You can also place a tack profit order at 107 linked to your initial conditional buy order, so that once you buy order is executed and you buy at 106, a take profit order will be executed only if the price reaches 107 or above.  If the price never reaches 106, neither your market buy order or take profit order will hit the market and you won't buy or sell anything. This is to protect your position in specific highly volatile market conditions.  If the stock is free falling and you only have a stop order at $90, it's possible that this order could be filled at $50 or even less. The limit is to protect you from that, as there are certain very specific times where it's better to just hold the stock instead of taking a huge loss (ie when price is whipsawing).