Exchange traded funds offer investors the opportunity to quickly and easily diversify their portfolios with broad market plays or focus on niche sectors picks.

To start off, investors can gain broad market exposure through cheap “total” ETFs that cover thousands of stocks, writes Nellie S. Huang for Kiplinger.

For instance, Vanguard Total Stock Market ETF (NYSEArca: VTI) holds over 3,000 large, midsize and small U.S. companies and comes with a low 0.05% expense ratio. Additionally, the Vanguard Total International Stock ETF (NYSEArca: VXUS) tracks over 5,000 developed and emerging stocks and has a 0.14% expense ratio. [Total Stock ETFs: A One-Stop Investment for Portfolio Diversification]

On the fixed-income side of your investment portfolio, something like the Vanguard Total Bond Market ETF (NYSEArca: BND) and Vanguard Total International Bond ETF (NYSEArca: BNDX) provide exposure to diversified U.S. and international debt. BND has a 0.08% expense ratio and BNDX has a 0.20% expense ratio. [Craft An Investment Portfolio Using 5 ETFs]

If an investor wants to customize his or her exposure, there are plenty of options as well.

For example, investors can break down asset class categories into large-, mid- and small-cap, with the Schwab U.S. Large-Cap ETF (NYSEArca: SCHX), which has a 0.04% expense ratio, iShares Russell Mid-cap ETF (NYSEArca: IWR), which has a 0.22% expense ratio and Vanguard Small Cap ETF (NYSEArca: VB), which has a 0.09% expense ratio.

Investors can also target specific sectors. The energy sector has been outperforming this year, and investors can capture the growth through a sector ETF like the Vanguard Energy ETF (NYSEArca: VDE). VDE is up 13.7% year-to-date.