Basically the actions serve to divide the expenses of a company. When somebody the purchase, the paid money is injected in the company, guaranteeing capital so that the same one grows. What the owner of the actions receives in exchange is the profit sharing. Therefore the actions suffer high and low the time all, therefore if the company tends to go badly or if the economy of the country enters in crisis, the people starts to vender them and the price of the same ones falls, therefore nobody wants to invest in a bad business. However, when the company is well in the market and has a profit expectation, its price is raised since it offers financial return. In few words, the price of the actions is controlled for the factor offers and looks for, as well as for the forecasts of the situation of the companies and the markets, that depends very, in our globalizado world, of the economic stability of the country.