Exchange traded funds (ETFs) could have another competitor if things keep going the way they are: exchange traded notes (ETNs).

The industry was once small, but has slowly been picking up steam. The first ETNs launched in 2006, by Barclays Bank PLC of London, says David Hoffman for Investment News.

They’re so attractive primarily because they give investors access to hard-to-reach markets. It also gives investors that access while they wait for an ETF equivalent. For example, India was covered by the iPath MSCI India Index ETN (INP) for a couple years before two India ETFs were launched earlier this year: the WisdomTree India Earnings (EPI) and the PowerShares India (PIN).

Of course, that doesn’t mean that just because there’s an ETN there will automatically be an ETF.