Millennials are now the largest generation in the U.S. workforce, making up 35% of workers, according to Pew Research. Yet these employees are still an enigma to many HR professionals and senior leaders trying to understand how to recruit and retain them. In fact, a Gallup poll shows that only 29% of millennials are engaged at work, and only half plan to be with their current company one year from now. The cost of this millennial turnover to business is a stunning $30.5 billion per year.

But it isn’t just millennials. A broader Gallup report states only 34% of American workers are engaged, and half are actively searching for a new job. The cost of lost productivity and high turnover of an entire workforce is an inconceivable $600-plus billion per year.

CEOs and CHROs are seeing these challenges impact their organizations. In one survey, 47% of CEOs and CHROs said they anticipate their best employees will quit within two years of hire.