They may not realize it, but the Sussexes just joined one of the hottest trends on Wall Street.

The freshly minted “impact partners” in the more than $1 billion asset manager Ethic are the latest members of the bespoke indexing movement that’s reshaping the U.S. investment industry. The fintech firm, in which Prince Harry and Meghan Markle are investors, builds custom indexes to ride the boom in environmental, social, and governance investing.

As new technology and cheaper trading proliferate, money managers are betting the next big thing is offering clients the benefits of indexing—like cheap trading costs and diversification—tailored to specific tastes.

In the past few weeks alone, Franklin Resources Inc. bought $6.4 billion money manager O’Shaughnessy Asset Management, including the firm’s custom-indexing business known as Canvas, while quant giant Dimensional Fund Advisors slashed the minimum for its separately managed accounts, or SMAs.

That all followed Vanguard’s purchase of direct indexer Just Invest in July—the asset giant’s first-ever acquisition.

“The technology behind direct indexing is making the investment minimums and costs of running these accounts fall like a rock,” said James Seyffart, an ETF analyst at Bloomberg Intelligence.

Morgan Stanley spent $7 billion on Eaton Vance Corp. last year, which owned Parametric Portfolio Associates—one of the heavyweights in direct indexing. BlackRock Inc.’s $1 billion purchase of Aperio, a creator of tailored index strategies, quickly followed.

The terminology is often ill-defined or confusing, but roughly the approaches look like this:

In direct indexing, investors buy the actual stocks in a particular benchmark rather than buy into a fund that bundles the shares together. That allows them to tweak the portfolio to tilt the weightings, or to harvest tax losses at the individual stock level.
Custom indexing is more fundamental and involves designing a gauge to meet the specific requirements of investors.

SMAs have been around for years. They are accounts managed by a professional investment firms to deliver customzed strategies to usually wealthy clients. Improving technology and falling trading costs are helping make them more accessible.

“My husband has been saying for years, ‘Gosh, don’t you wish there was a place where if your values were aligned like this, you could put your money to that same sort of thing?’” Markle told The New York Times’ DealBook.

This article was provided by Bloomberg News.