A public company is a company whose ownership is organized via shares of stock which are intended to be freely traded on a stock exchange or in over-the-counter markets. A public (publicly traded) company can be listed on a stock exchange (listed company), which facilitates the trade of shares, or not (unlisted public company). In some jurisdictions, public companies over a certain size must be listed on an exchange. In most cases, public companies are private enterprises in the private sector, and "public" emphasizes their reporting and trading on the public markets.

Public companies are formed within the legal systems of particular states and so have associations and formal designations, which are distinct and separate in the polity in which they reside. In the United States, for example, a public company is usually a type of corporation, though a corporation need not be a public company. In the United Kingdom, it is usually a public limited company (PLC). In France, it is a société anonyme (SA). In Germany, it is an Aktiengesellschaft (AG). While the general idea of a public company may be similar, the differences between types are meaningful and are at the core of international law disputes with regard to industry and trade.

Usually, the securities of a publicly traded company are owned by many investors while the shares of a privately held company are owned by relatively few shareholders. A company with many shareholders is not necessarily a publicly traded company. Conversely, a publicly traded company typically (but not necessarily) has many shareholders. In the United States, companies with over 500 shareholders in some instances are required to report under the Securities Exchange Act of 1934; companies that report under the 1934 Act are generally deemed public companies.^{[citation needed]}

A public company possess some advantages over privately held businesses.

Many stock exchanges require that publicly traded companies have their accounts regularly audited by outside auditors and then publish the accounts to their shareholders. Besides the cost, that may make useful information available to competitors. Various other annual and quarterly reports are also required by law. In the United States, the Sarbanes–Oxley Act imposes additional requirements. The requirement for audited books is not imposed by the exchange known as OTC Pink. The shares may be maliciously held by outside shareholders and the original founders or owners may lose benefits and control. The principal–agent problem, or the agency problem is a key weakness of public companies. The separation of a company's ownership and control is especially prevalent in such countries as the United Kingdom and the United States.

In the United States, the Securities and Exchange Commission requires firms whose stock is traded publicly to report their major shareholders each year. The reports identify all institutional shareholders (primarily firms that own stock in other companies), all company officials who own shares in their firm, and all individuals or institutions owning more than 5% of the firm's stock.

For many years, newly created companies were initially privately held but later held initial public offerings to become publicly traded companies or to be acquired by another company if they became larger and more profitable or had promising prospects. More infrequently, some companies such as the investment banking firm Goldman Sachs and the logistics services provider United Parcel Service (UPS) chose to remain privately held for a long period of time after maturity into a profitable company.

However, from 1997 to 2012, the number of corporations publicly traded on US stock exchanges dropped 45%. According to one observer (Gerald F. Davis), "public corporations have become less concentrated, less integrated, less interconnected at the top, shorter lived, less remunerative for average investors, and less prevalent since the turn of the 21st century".