Bain and company employeesBain employees, or “Bainies,” sit in the New York office’s kitchen.GlassdoorTwo tech companies and a consulting firm make an unusual trio, but according to the employer review site Glassdoor they share one key distinction.

Google, Facebook, and Bain & Company are the three best workplaces in the US.

Since 2009, when Glassdoor began collecting data for its Best Places to Work ranking, the three companies have consistently made the list, and lately they’ve stayed ins the top 10. Facebook was ranked the best workplace of 2018, Bain & Co. was ranked the best workplace of 2017, and Google was the best of 2015.

There are a number of ways to explain what makes the companies great. Here are the biggest factors.