Millennials are going all-in when it comes to using exchange-traded funds in their investment portfolios.

In fact, almost everyone — 96 percent — who responded to a recent Charles Schwab survey said they considered the passive index-tracking securities “a necessary part” of their investment strategy, and 91 percent said ETFs are their “investment vehicle of choice.”

The move is coming at the expense of individual stocks, with more than half of millennials surveyed saying they dumped all their equity holdings for ETFs.

Passive investing, which involves using funds that track market indexes like the S&P 500, the Dow industrials, and multiple other trackers and strategies, has surged in popularity over the past decade. Assets held by the industry have surged from $531 billion in 2008 to more than $3.4 trillion currently, according to Statista.

Growth has occurred across age groups but has been particularly strong among the youngest cohort, which grew up in an era in which indexing became vogue. Investors prefer the funds for their ease of trading and low costs compared with mutual funds.

Read the rest of the article at CNBC.com.