As the world's richest individuals approach retirement, the next three decades will see trillions fall into the hands of their younger family members—the biggest wealth transfer in history from one generation to the next, according to a new report.

At least $16 trillion of ultra-high net worth (UHNW) individual's wealth will be passed on to the next generation over this period, spawning a new crop of multimillionaires, the Wealth-X and NFP Family Wealth Transfers Report published on Tuesday said.

"As self-made UHNW baby boomers start passing on their wealth to their children, the importance of entrepreneurship and hard work will be put to the test," the report said.

The world's population of ultra high-net worth individuals—those with at least $30 million in assets—grew to 211,235 last year, with a combined wealth of $29.7 trillion, a record high for both population and wealth.

The U.S., home to the largest billionaire population, will see the greatest amount of wealth transfers, with $6 trillion set to change hands over the next 30 years.

Germany, Japan, the U.K. and Brazil follow as the countries with the largest expected wealth transfers—a target for estate planners.

