What is a Fortune 500 Company?

The Fortune 500 has changed dramatically over the decades. Source: Fortune.

Fortunemagazine has been publishing its Fortune 500 list every year since 1955. But what exactly is a Fortune 500 company? What does it take to make the cut? How is it chosen, and by whom?

Let's take a closer look at the Fortune 500 and answer all of your questions, and maybe a few you didn't know to ask.

What is the Fortune 500?The Fortune 500 is a rank of U.S. companiesby total sales that's chosen byFortune's editorseach year. More specifically, the list includes U.S. companies that file financial statements with a financial regulatory agency. As such, it principally showcases publicly trade companies, though not exclusively. For example, you have to go all the way to State Farm Insurance at No. 41 before coming across a privately owned firm.

In the short run, the companies at or near the top of the Fortune 500 tend to stay the samefrom one year to the next -- though, the order may change a bit, and mergers and acquisitions can occasionally shake things up. The top heavyweights over the past 15 years, for instance, wereExxonMobil andWal-Mart, which have rotated back and forth between the top two spots, largely depending on oil prices.

Wal-Mart's 6,000-truck fleet runs millions of miles. Advanced technologies could save it big bucks.

Many of DuPont's most innovative products like nylon weren't developed until more than a century after the company's founding. Source: DuPont.

Over longer periods of time, alternatively, the list has changed dramatically. According to Fortune, there are only 57 companies that have been on the list since the beginning.

Of the top 10 companies on the inaugural list, onlyE. I. du Pont de Nemours and Company-- you know it as DuPont -- and GeneralElectrichave not been acquired, merged, or filed for bankruptcy.

Here's the top-10 list by industry in 1955:

3 oil companies
2 automakers
1 conglomerate (which owned meatpacking, car rental, and consumer goods businesses)
1 industrial manufacturer
1 steelmaker
1 meatpacker
1 chemical manufacturer.

And here's the list in 2015:

3 oil companies
2 automakers
1 conglomerate (insurance, consumer goods, manufacturing, transportation)
1 industrial manufacturer
1 retail store operator
1 electronics manufacturer
1 drug store operator and health services provider.

Staying power Of the companies on the original list, there are a few mainstays that have been around nearly as long as America itself.

Bank of New York Mellon Corp(No. 189 on this year's list) was founded in 1784 by Alexander Hamilton. This was less than one year after the Treaty of Paris between the newly independent America and Britain, and several years before the U.S. Constitution would be ratified.

Colgate-Palmolive products have been mainstays in consumers' homes for more than two centuries. Image sources: Colgate-Palmolive.

DuPont also had its founding early in American history, beginning as a gunpowder mill in 1802. Within 50 years it would be the largest supplier of gunpowder to the U.S. military, and would remain largely a gunpowder and explosives manufacturer for more than a century before diversifying in the early 1900s. Today, DuPont is one of the foremost chemical companies in the world, and a mainstay of the top-100 on this list.

Other notable companies in the Fortune 500 that have been around for more than a century include retailerMacy's(founded in 1830), financial services companyState Street(1792), consumer goods giant Colgate-Palmolive(1806),and pharmaceutical company McKesson, founded in 1833 as Olcott & McKesson.

. Of the 57 still on the list, many have remained through innovation, like DuPont, while others like Colgate-Palmolive have continued providing consumers with necessities like toothpaste and soap.

Amazingly, of the top 10 companies on the first list in 1955, three were in the top 10 in 2015:ExxonMobilwas second place (Exxon) and ninth (Mobil) on the first list, and took the top spot on the most recent list; sixth-placeGeneral Motorswas number one on the inaugural list; and General Electricwas fourth in 1955, and eighth on the 2015 list. Of course, GE is the only company that's really the "same", with ExxonMobil being a merger of two former top-10 companies, and GM having gone bankrupt only a few years ago, wiping out shareholders when it reorganized.

What will the Fortune 500 look like in another 61 years?When the inaugural list was rolled out six decades ago, companies that have become mainstays of the top 100 -- such as Amazon,Microsoft, and Google --weren't even a twinkle in their founders' eyes; but consolidation, changing consumer tastes, and the impact of new technologies have changed the mix of industries that populate the list.

How many technical innovations will change the face of the list in years to come? That's a question only time will answer, but it's sure going to be fun following it.

The article What is a Fortune 500 Company? originally appeared on Fool.com.

Jason Hall owns shares of Organovo, Amazon.com, and Google (A shares). The Motley Fool recommends Amazon.com, General Motors, Google (A shares), Google (C shares), and McKesson. The Motley Fool owns shares of Amazon.com, ExxonMobil, General Electric Company, Google (A shares), and Google (C shares). Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.