Some indexes contain thousands of bonds such as the Morningstar Core Bond Index, while others, like the Barclay’s I Share Aggregate Bond Fund Index, include just a few dozens. Like stock ETFs, bond...

Some indexes contain thousands of bonds such as the Morningstar Core Bond Index, while others, like the Barclay’s I Share Aggregate Bond Fund Index, include just a few dozens. Like stock ETFs, bond funds give investors low fees, transparency, and flexibility.