A list of companies within a particular industry can be helpful for a variety of reasons: you may use the list to find the biggest/most impactful companies in a market/industry, to find a list of competitors, to pitch a product or service, or to network with/apply to.
Tip: Be sure to understand how any rankings or lists are compiled, and what companies are included. For instance, Mergent Online defaults to showing only public US companies as competitors.
Source: Mergent Online database