A subsidiary company, subsidiary, or daughter company is a company that is completely or partly owned and wholly controlled by another company that owns more than half of the subsidiary's stock. The subsidiary can be a company, corporation, or limited liability company. In some cases it is a government or state-owned enterprise. The controlling entity is called its parent company, parent, or holding company.

An operating subsidiary is a business term frequently used within the United States railroad industry. In the case of a railroad, it refers to a company that is a subsidiary but operates with its own identity, locomotives and rolling stock. In contrast, a non-operating subsidiary would exist on paper only (i.e. stocks, bonds, articles of incorporation) and would use the identity and rolling stock of the parent company.

Subsidiaries are a common feature of business life, and all multinational corporations organize their operations in this way. Examples include holding companies such as Berkshire Hathaway as in this listing of its subsidiaries, Time Warner, or Citigroup; as well as more focused companies such as IBM, or Xerox Corporation. These, and others, organize their businesses into national and functional subsidiaries, oftentimes with multiple levels of subsidiaries.

In the fictional world of Iron Man, Stark Industries, later also known as Stark International, Stark Innovations, Stark/Fujikawa, Stark Enterprises and currently Stark Resilient, is a fictional multi-billion dollar corporation owned and run by businessman Anthony Edward "Tony" Stark, also known as Iron Man. The company appears in stories published by Marvel Comics. It first appeared in Tales of Suspense #40 and was founded by Howard Stark, Tony's father. According to Forbes 25 largest fictional companies it had an estimated sales of $20.3 billion. In the film version of Iron Man, Stark Industries has a logo similar to that of defense contractors Lockheed Martin and Northrop Grumman and is listed on the New York Stock Exchange as SIA. During the press conference scene, Stark is seen entering a building that resembles the entrance to Lockheed Martin's Skunk Works facility. An airplane extremely similar to the Northrop YF-23 stood as a statue in front of the Stark Industries facility, exactly like the prototype on display at one of Northrop Grumman's facilities at the time of the movie's filming. In Iron Man Armored Adventures, it is shown that Tony Stark finally has decided to create his own company along with Pepper Potts and James (Rhodey) Rhodes, the name of the company is called Stark Solutions.