Here are a few suggestions that are good to start with regardless of what you are looking for and what company or companies you are looking to research.
First, if you haven't done so and if there is one, go to the company's website. Companies will often organize their website in ways that can provide a sense of how they do business. If the company has an About Us area, that may be where they provide a company overview, history information, etc.. Also, if they are a public company check to see if they have an Investor Relations page. This area will likely include a number of financial reports and filings as well as other corporate information like information on executives, location information, history, etc. For private companies, their web page may be the best source of information on products, organization, locations, etc.
The next stop may be to look for directories either in print or as a database. This may seem basic, but they can still be quite important. Depending on the data gathered, the formatting and/or the search options, or the intent, these directory sources may provide details that just aren't found on a company website like competitors, sales/employee figures, etc. Electronic products can do even more for researchers by allowing them to tailor their search and their output. Because there are so many company and industry directories, what we have included here is not a comprehensive list but are likely to be some of the more common resources.
Historically, directories came out in print. This meant a delay in the data and a limit to the ways users could use the title. However, with the advent of electronic databases, things have changed. These databases allow researchers to determine what they want their list to look like. Databases like Mergent Intellect, ReferenceUSA, and many others allow users to limit their search to a specific geography (city, state, metro area, etc), industry, company type, etc. in order for them to get the list that is tailored to their specific needs.
While many directories have moved online only, there are still many published in print as well. These are some of the more general and often most accessible and available directories in local public or university libraries.
Below are selected Library of Congress Subject Headings (LCSH) that may be useful for searching regional as well as universal/general purpose directories. Also, many directories can cover specific industries. An example related to insurance companies include Best's Insurance Reports: Property / Casualty and Best's Insurance Reports: Life / Health. If you need to look for directories for specific industry you can do a keyword search in only the subject headings. Most links below go to the Library of Congress Online Catalog.