There is nearly $13 trillion invested in exchange-traded funds, or ETFs. ETFs that mirror the S&P 500. ETFs for gold. ETFs for bitcoin. There’s even a Vegan ETF. How did this market get so big and varied? And just what goes into one?

On today’s podcast, our Bloomberg Explains series continues with Bloomberg Intelligence senior ETF analyst and co-host of the Trillions podcast Eric Balchunas. He tells host David Gura about the unlikely duo who created the first-ever ETF in a last-ditch bid to save a struggling exchange. And Bloomberg ETF IQ and Money Stuff co-host Katie Greifeld breaks down the current booming market, and outlines which ETFs are safe investments – and which are better left alone. 

Further listening: Trillions Podcast - Bloomberg,  Money Stuff - Bloomberg