How does an enlarged share base affect share price?
Most of the time when a stock splits to create more shares, it is done to bring the price per share down to a level that makes potential investors more comfortable. There are psychological reasons why some companies keep the price in the $30 to $60 range. Others like to have the price keep rising into the hundreds or thousands a share.  The split doesn't help current investors, with the possible exception that the news spurs interest in the stock which leads to a short term rise in prices; but it also doesn't hurt current investors. When a reverse stock split is done, the purpose is for one of several reasons:
The company's value (which should be reflected in the share price) is not how much money it has in the bank, but something along the lines of 'how much money will it make between now and the end of times' (adjusted for time value of money and risk). So when you purchase a share of a company that has, say, little money in the bank, but expects to make 1M$ profit this year, 2M$ for the following 3 years, and say, nothing after, you are going to pay your fraction of 7M$ (minus some discount because of the risk involved). If now they announce that their profits were only 750k$, then people may think that the 2M$ are more likely to be 1.5M$, so the company's value would go to ~ 5M$. And with that, the market may perceive the company as more risky, because its profits deviated from what was expected, which in turn may reduce the company's value even further. "Share price is based on demand.  Assuming the same amount of shares are made available for trade then stocks with a higher demand will have a higher price.  So say a company has 1000 shares in total and that company needs to raise $100. They decide to sell 100 shares for $1 to raise their $100. If there is demand for 100 shares for at least $1 then they achieve their goal. But if the market decides the shares in this company are only worth 50 cents then the company only raises $50. So where do they get the other $50 they needed? Well one option is to sell another 100 shares. The dilution comes about because in the first scenario the company retains ownership of 900 or 90% of the equity. In the second scenario it retains ownership of only 800 shares or 80% of the equity. The benefit to the company and shareholders of a higher price is basically just math. Any multiple of shares times a higher price means there is more value to owning those shares. Therefore they can sell fewer shares to raise the same amount.  A lot of starts up offer employees shares as part of their remuneration package because cash flow is typically tight when starting a new business. So if you're trying to attract the best and brightest it's easier to offer them shares if they are worth more than those of company with a similar opportunity down the road. Share price can also act as something of a credit score. In that a higher share price ""may"" reflect a more credit worthy company and therefore ""may"" make it easier for that company to obtain credit. All else being equal, it also makes it more expensive for a competitor to take over a company the higher the share price. So it can offer some defensive and offensive advantages. All ceteris paribus of course." There has been a lot of research on the effects of stock splits. Some studies have concluded that: However note that (i) these are averages over large samples and does not say it will work on every split and (ii) most of the research is a bit dated and more recent papers have often struggled to find any significant performance impact after 1990, possibly because the effect has been well documented and the arbitrage no longer exists. This document summarises the existing research on the subject although it seems to miss some of the more recent papers. More practically, if you pay a commission per share, you will pay more commissions after the split than before. Bottom line: don't overthink it and focus on other criteria to decide when/whether to invest. isn't it still a dilution of existing share holder stock value ? Whether this is dilution or benefit, only time will tell. The Existing value of Facebook is P, the anticipated value after Watsapp is P+Q ... it may go up or go down depending on whether it turns out to be the right decision. Plus if Facebook hadn't bought Watsapp and someone else may have bought and Facebook itself would have got diluted, just like Google Shadowed Microsoft and Facebook shadowed Google ... There are regulations in place to ensure that there is no diversion of funds and shady deals where only the management profits and others are at loss. Edit to littleadv's comments: If a company A is owned by 10 people for $ 10 with total value $100, each has 10% of the share in the said company. Now if a Company B is acquired again 10 ea with total value 100. In percentage terms everyone now owns 5% of the new combined company C. He still owns $10 worth. Just after this acquisition or some time later ... Stock trading (as opposed to IPO) doesn't directly benefit the company. But it affects their ability to raise additional funds; if they're valued higher, they don't need to sell as many shares to raise a given amount of money.  And the stockholders are part owners of the company; their votes in annual corporate meetings and the like can add up to a substantial influence on the company's policies, so the company has an interest in keeping them (reasonably) happy. Dividends (distributing part of the company's profits to the stockholders) are one way of doing so. You're still investing in the company. The fact that you're buying someone else's share just means you're doing so indirectly, and they're dis-investing at the same time. Like others have already said, it may cause an immediate dip due to a large and sudden move in shares for that particular stock. However, if there is nothing else affecting the company's financials and investors perceive no other risks, it will probably bounce back a bit, but not back to the full value before the shares were issued. Why? Whenever a company issues more stock, the new shares dilute the value of the current shares outstanding, simply because there are now more shares of that stock trading on the market; the Earnings Per Share (EPS) Ratio will drop since the same profit and company value has to be spread across more shares. Example:  If a company is valued at $100 dollars and they have 25 shares outstanding, then the EPS ratio equates to $4 per share (100/25 = 4).  If the company then issues more shares (stock to employees who sell or keep them), let's say 25 more shares, then shares outstanding increase to 50, but the company's value still remains at $100 dollars. EPS now equates to $2 per share (100/50 = 2). Now, sometimes when shareholders (especially employees...and especially employees who just received them) suddenly all sell their shares, this causes a micro-panic in the market because investors believe the employees know something bad about the company that they don't. Other common shareholders then want to dump their holdings for fear of impending collapse in the company. This could cause the share price to dip a bit below the new diluted value, but again if no real, immediate risks exist, the price should go back up to the new, diluted value. Example 2: If EPS was at $4 before issuing more stock, and then dropped to $2 after issuing new stock, the micro-panic may cause the EPS to drop below $2 and then soon rebound back to $2 or more when investors realize no actual risk exists. After the dilution phase plays out, the EPS could actually even go above the pre-issuing value of $4 because investors may believe that since more stock was issued due to good profits, more profits may ensue. Hope that helps! You can calculate the fully diluted shares by comparing EPS vs diluted (adjusted) EPS as reported in 10K. I don't believe they report the number directly, but it is a trivial math exercise to reach it. The do report outstanding common stock (basis for EPS). "Thanks for pointing out [the study](http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1748851). It's a slightly different cause than what I was describing when I posted this. Specifically, they show an effect not when the names get confused, but rather when the name similarity simply brings more attention to the stock. I was surprised nobody mentioned that in response to my post.  But also interesting is that they had to control for simple confusion between stock symbols, which implies that ticker confusion has a known effect. So I dug into research on that and quickly found [this study](http://www.efmaefm.org/0EFMAMEETINGS/EFMA%20ANNUAL%20MEETINGS/2010-Aarhus/EFMA2010_0161_fullpaper.pdf) found ""a high positive correlation between returns on two matching stocks with similar ticker symbols""." It means $400m expected revenue, likely spread out over multiple years as it gets implemented, and not entirely guaranteed to happen as they still need to fulfill the contract. The impact on the stock price is complex - it should be positive, but nowhere close to a $400m increase in market cap. If the company is expected to routinely win such contracts, it may have no significant effect on the stock price, as it's already priced in - say, if analysts expect the company to win 1.2b contracts in this fiscal year, and now they've done 1/3 of that, as expected. How I understand it is: supply/demand affect price of stock   negatively/positively, respectively. Correct. Volume is the amount of buying/selling activity in these stocks (more   volume = more fluctuation, right?). Sort of.  Higher volume means higher liquidity.  That is, a stock that is traded more is easier to trade.  It doesn't necessarily mean more fluctuation and in the real world, it often means that these are well-understood stocks with a high amount of analyst coverage.  This tends towards these stocks not being as volatile as smaller stocks with less liquidity. Company revenue (and profit) will help an investor predict company   growth. That is one factor in a stock price.  There are certain stocks that you would buy without them making a profit because their future revenue looks potentially explosive.  However, these stocks are very risky and are bubble-prone. If you're starting out in the share market, it's generally a good idea to invest in index funds (I am not a broker, my advice should not be taken as financial advice).  These funds aggregate risk by holding a lot of different companies.  Also, statistics have shown that over time, buying and holding index funds long term tends to dramatically outperform other investment strategies, particularly for people with low amounts of capital. Yes, it does matter. You are right that lower demand for a stock will drive its price down. Lower stock prices can hurt the company. Take a look at Fixee's answer to this question: a declining share price will make it hard to secure credit, attract further investors, build partnerships, etc. Also, employees are often holding options or in a stock purchase plan, so a declining share price can severely dampen morale. In an extreme case, if share prices plummet too far, the company can be pressured to reverse-split the shares, and (eventually) take the company private. This recently happened to Playboy. If you do not want to support a company, for whatever reason, then it is wise to avoid their stock. Companies with existing borrowings (where borrowings are on variable interest rates) or in the case with fixed interest rates - companies that get new borrowings - would pay less interest on these borrowings, so their cost will go down and profits up, making them more attractive to investors.  So, in general lower interest rates will make the share market a more attractive investment (than some alternatives) as investors are willing to take on more risk for potentially higher returns. This will usually result in the stock market rising as it is currently in the US. EDIT: The case for rising interest rates A central bank's purpose when raising interest rates is to slow down an economy that is booming. As interest rates rise consumers will tighten up their spending and companies will thus have less revenue on top of higher costs for maintaining existing borrowing (with variable rates) or new borrowing (with fixed rates). If rates are higher companies may also defer new borrowings to expand their business. This will eventually lead to lower profits and lower valuation for these companies. Another thing that happens is that as banks start increasing interest for saving accounts investors will look for safety where they can get a higher return (than before) without the risk of the stock market.  With lowering profits and valuations, and investor's money flowing out of shares and into the money market, so will company share prices drop (although this may lag a bit with the share market still booming due to greed. But once the boom stops watchout for the crash). "The price of a company's stock at any given moment is established by a ratio of buyers to sellers.  When the sellers outnumber the buyers at a given price, the stock price drops until there are enough people willing to buy the stock to balance the equation again.  When there are more people wanting to purchase a stock at a given price than people willing to sell it, the stock price rises until there are enough sellers to balance things again.  So given this, it's easy to see that a very large fund (or collection of very large funds) buying or selling could drive the price of a stock in one direction or another (because the sheer number of shares they trade can tip the balance one way or another).   What's important to keep in mind though is that the ratio of buyers to sellers at any given moment is determined by ""market sentiment"" and speculation.  People selling a stock think the price is going down, and people buying it think it's going up; and these beliefs are strongly influenced by news coverage and available information relating to the company.  So in the case of your company in the example that would be expected to triple in value in the next year; if everyone agreed that this was correct then the stock would triple almost instantly.  The only reason the stock doesn't reach this value instantly is that the market is split between people thinking this is going to happen and people who think it won't.   Over time, news coverage and new information will cause one side to appear more correct than the other and the balance will shift to drive the price up or down.  All this is to say that YES, large funds and their movements CAN influence a stock's trading value; BUT their movements are based upon the same news, information, analysis and sentiment as the rest of the market.  Meaning that the price of a stock is much more closely tied to news and available information than day to day trading volumes.  In short, buying good companies at good prices is just as ""good"" as it's ever been.   Also keep in mind that the fact that YOU can buy and sell stocks without having a huge impact on price is an ADVANTAGE that you have.  By slipping in or out at the right times in major market movements you can do things that a massive investment fund simply cannot." More shares mean less volatility because it takes a larger number of trades, a larger number of shares per trade, or a combination of both to raise or lower the stock price. Institutional investors (mutual funds, pensions, hedge funds, other investment firms, etc) are the sorts of organizations with the large amounts of money needed to move a stock price one way or the other.  But the more floating shares there are in a company, the harder it is for one or two firms to move a stock price.  A company with fewer floating shares wouldn't require as many trades (or as many shares per trade) to see wider swings in price. When it comes to stock price, insider trading isn't the same as manipulation.  In the (surprisingly few) cases of insider trading that are prosecuted, it tends to be an individual (or small group) with early access to information that the broader market doesn't have being able to buy or sell ahead of the broader market.  Their individual sales are seldom if ever enough to noticeably move a stock price.  They're locking in profit or limiting a loss.  Manipulation might (but doesn't always) precede insider trading, if misinformation (or truth) is released for the purpose of creating a situation that can be profited from via a trade or trades. "I don't have anything definitive, but in general positions in a company are not affected materially by what is called a corporate action. ""Corp Actions"" can really be anything that affects the details of a stock. Common examples are a ticker change, or exchange change, IPO (ie a new ticker), doing a split, or merging with another ticker. All of these events do not change the total value of people's positions. If a stock splits, you might have more shares, but they are worth less per share. A merger is quite similar to a split. The old company's stock is converted two the new companies stock at some ratio (ie 10 shares become 1 share) and then converted 1-to-1 to the new symbol. Shorting a stock that splits is no different. You shorted 10 shares, but after the split those are now 100 shares, when you exit the position you have to deliver back 100 ""new"" shares, though dollar-for-dollar they are the same total value. I don't see why a merger would affect your short position. The only difference is you are now shorting a different company, so when you exit the position you'll have to deliver shares of the new company back to the brokerage where you ""borrowed"" the shares you shorted."