Public companies sell shares of the company (stocks) to the general public and are required to make public their financial information along with certain specific details about the company's operations, compensation, ownership, etc. Reporting requirements vary from country to country - in the US, these reports are submitted to the Securities and Exchange Commission (SEC) and the SEC makes these available to the public on the SEC website.
In the US, companies file annual 10-Ks with SEC - these are the best source for company information about directors and officers, their pay and share ownership of company, legal proceedings, locations of properties, company products, strategies, alliances, and more. Property locations and principal plants, mines and other important properties are reported, and whether or not they are leased or owned. Companies post their 10-Ks on their websites under Investor Relations.These SEC documents are available in most company information databases listed in this guide. See SEC's consumer focused guide to how to read a company's 10-K which details all the different sections and where to find relevant information. Investopedia has a guide to other reports that are required of companies - such as when insiders sell stock or someone buys more than 5% of a company's stocks or other unscheduled important events take place within the company.
Subsidiaries of public companies: the parent company is not required to report on each of these individually. Information can be found in reports of the parent company and from other business news sources.
Private companies are not required to release information to the general public and generally only basic company information is available. Other information may be found in business and other news sources.
Databases for company information