There’s no doubt that when it comes to providing jobs, the Fortune 500 is a vital cog in the nation’s economic engine. All together, companies on the list employed nearly 27 million people last year, which represents about 17% of the nation’s overall workforce—a figure that’s been relatively constant for the last 20 years.

Some Fortune 500 companies, of course, employ more people than others. Employers in the labor-intensive retail industry tend to have mammoth rosters of sales associates, cashiers, and warehouse workers. That’s evident when you look at the list of top companies ranked by number of employees, where four of the top seven are retail giants.

It’s important to note that these companies’ status as the Fortune 500’s biggest employers doesn’t necessarily mean that their employee ranks are growing. Here’s a look at the top seven on the 2015 Fortune 500 list and how their head counts have fared over the past 10 years.