NEW YORK (TheStreet) -- ETFs have grown 25% a year since 2002 and many experts see this growth continuing in the future.1In addition to taking over a larger share of the broad market, ETFs could also grow in terms of complexity and structure. As index-based trading becomes more popular, as in the ETF market, ETF sponsors and index providers will "push to develop new and interesting indexes," says Michael Mundt, a partner at the law firm Stradley Ronon Stevens & Young and a former assistant director at the SEC who worked on ETF issues. Currently, ETFs track major indices, bonds, commodities, derivatives, industries or even specific market caps. As investors demand more ETFs, more differentiation will emerge in the baskets of securities that ETFs track. One area that has the "greatest potential for growth" is in actively managed ETFs, according to Mundt.