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Did an additional $32 billion necessarily get invested into Amazon.com stock on October 26th, 2017?
The market capitalization of a stock is the number of shares outstanding (of each stock class), times the price of last trade (of each stock class). In a liquid market (where there are lots of buyers and sellers at all price points), this represents the price that is between what people are bidding for the stock and what people are asking for the stock.  If you offer any small amount more than the last price, there will be a seller, and if you ask any small amount less than the last price, there will be a buyer, at least for a small amount of stock. Thus, in a liquid market, everyone who owns the stock doesn't want to sell at least some of their stock for a bit less than the last trade price, and everyone who doesn't have the stock doesn't want to buy some of the stock for a bit more than the last trade price. With those assumptions, and a low-friction trading environment, we can say that the last trade value is a good midpoint of what people think one share is worth.  If we then multiply it by the number of shares, we get an approximation of what the company is worth. In no way, shape or form does it not mean that there is 32 billion more invested in the company, or even used to purchase stock. There are situations where a 32 billion market cap swing could mean 32 billion more money was invested in the company: the company issues a pile of new shares, and takes in the resulting money.  People are completely neutral about this gathering in of cash in exchange for dilluting shares.  So the share price remains unchanged, the company gains 32 billion dollars, and there are now more shares outstanding. Now, in some sense, there is zero dollars currently invested in a stock; when you buy a stock, you no longer have the money, and the money goes to the person who no longer has the stock. The issue here is the use of the continuous tense of "invested in"; the investment was made at some point, but the money doesn't really stay in this continuous state of being.  Unless you consider the investment liquid, and the option to take money out being implicit, it being a continuous action doesn't make much sense. Sometimes the money is invested in the company, when the company causes stocks to come into being and sells them. The owners of stocks has invested money in stocks in that they spent that money to buy the stocks, but the total sum of money ever spent on stocks for a given company is not really a useful value. The market capitalization is an approximation, which under the efficient market hypothesis (that markets find the correct price for things nearly instantly) is reasonably accurate, of the value the company has collectively to its shareholders.  The efficient market hypothesis isn't accurate, but it is an acceptable rule of thumb. Now, this value -- market capitalization -- is arguably not the total value of a company: other stakeholders include bond holders, labour, management, various contract counter-parties, government and customers.  Some companies are structured so that almost all value is captured not by the stock owners, but by contract counter-parties (this is sometimes used for hiding assets or debts). But for most large publically traded companies, it (in theory) shouldn't be far off.