The study looked at over a million French workers and their employing firms to understand what influences wages. They found that personal differences among workers, like skills and experience, play a big role in how much they get paid. Firms that hire high-wage workers tend to be more productive but not necessarily more profitable. Companies that pay higher wages are also more productive and profitable, and they tend to use more capital. Overall, personal differences explain most of the wage differences between industries and firm sizes, while firm differences have less impact.