The Federal Reserve hiked interest rates three times last year and more rate increases are expected this year. Still, 10-year Treasuries yield less than 2.7%, underscoring a nearly four-decade downtrend in U.S. borrowing costs. For its part, the S&P 500 yields an anemic 1.8%.

Those data points confirm that traditional options for income are likely to leave yield-hungry investors wanting more. Scores of exchange-traded funds (ETFs) can help investors shore up portfolio yield while increasing current and future income. Vanguard, the second-largest U.S. issuer of ETFs, offers some compelling income funds.

Vanguard’s income ETFs run the gamut from traditional dividend equity funds to basic bonds to more exotic fare, including international dividend stocks and even emerging markets debt.

Of course, many Vanguard dividend ETFs are among the least expensive in their respective categories, providing cost-conscious income investors with added ways to pinch pennies.

Vanguard ETFs: Vanguard Dividend Appreciation ETF (VIG)

Expense ratio: 0.08% annually, or $8 on a $10,000 investment.

SEC Yield: 1.8%

In terms of sheer size, the Vanguard Dividend Appreciation ETF (NYSEARCA:VIG) is the king of U.S. dividend ETFs, as this Vanguard ETF had $27.3 billion in assets under management at the end of 2017.

Two easily identifiable reasons highlight VIG’s popularity with income investors. First, this Vanguard fund charges just 0.08% per year, making it 92% cheaper than the average fees of competing strategies. Second, VIG mandates that member firms have dividend increase streaks of at least 10 years, which implies steady, dependable dividend growth over the long haul.

The rub with the dividend increase streak requirement is that it leaves VIG lightly allocated to tech stocks (just 9.6% of the ETF’s weight). Industrials account for over a third of this Vanguard ETF’s sector weight.

Vanguard ETFs: Vanguard High Dividend Yield ETF (VYM)

Expense ratio: 0.08%

SEC Yield: 2.4%

Like the aforementioned VIG, the Vanguard High Dividend Yield ETF (NYSEARCA:VYM) is one of the titans among U.S. dividend ETFs. $21.4 billion in assets under management confirms as much. VYM, which currently resides at record highs, is positioned as a high-yield dividend fund, but its trailing 12-month yield of 2.81% is not alarmingly high.

That is good news because while high dividend yields are seductive, they can also be warnings signs about shaky corporate financials or looming negative dividend actions. Additionally, VYM is lightly allocated to traditional high-yield sectors.

For example, telecom and utilities stocks combine for just 12.3% of this Vanguard ETF’s weight, well below the 15.6% allocated to technology stocks. Said another way, VYM’s weight to Microsoft Corporation (NASDAQ:MSFT) is triple its weight to Verizon Communications Inc. (NYSE:VZ).

Vanguard ETFs: Vanguard Emerging Markets Government Bond ETF (VWOB)

Expense Ratio: 0.32%

SEC Yield: 4.1%

Emerging markets bonds can be a tricky asset class to navigate, which is probably one reason why investors often turn to funds rather than attempting to pick individual issues. The Vanguard Emerging Markets Government Bond ETF (NASDAQ:VWOB) compensates investors for the risks associated with emerging markets debt as highlighted by a yield of over 4%.

Speaking of risks, there are some with this Vanguard ETF. VWOB allocates 19% of its combined weight to Mexican and Brazilian bonds. Mexico is widely expected to be the only emerging market to raise interest rates this year while Brazil recently suffered a credit downgrade, pushing its rating further into junk territory.

Over 55% of VWOB’s 1,029 holdings are rated A or Baa, but nearly 40% of this Vanguard fund’s holdings carry non-investment grade ratings.

Vanguard ETFs: Vanguard Global ex-US Real Estate ETF (VNQI)

Expense ratio: 0.15%

12-Month Yield: 3.7%

By focusing on U.S. real estate stocks and ETFs last year, some investors were left disappointed. For example, the popular Vanguard Real Estate ETF (NYSEARCA:VNQ) rose just 4.9% in 2017, a far cry from the 21.7% returned by the S&P 500.

That should serve as a reminder regarding the importance of removing domestic investing biases because the Vanguard Global ex-US Real Estate ETF (NASDAQ:VNQI) jumped nearly 27% last year while delivering less annualized volatility than the domestic VNQ.

VNQI, which yields nearly 4%, is off to the races to start 2018 with a gain of over 5%. This Vanguard ETF allocates over 43% of its weight to Japan, Hong Kong and China.

Vanguard ETFs: Vanguard International Dividend Appreciation ETF (VIGI)

Annual fee: 0.25%

12-month Yield: 1.8%

Not all sequels are worth seeing, but a case can be made that the Vanguard International Dividend Appreciation ETF (NASDAQ:VIGI) is on its way to becoming the Godfather II to VIG’s Godfather I. To clarify the cinematic reference, VIGI is the international answer to the aforementioned domestic VIG.

Investors are enthusiastic about VIGI. This Vanguard ETF was one of just two ETFs launched by the fund giant in 2016. Now, just a month shy of its second birthday, VIGI has nearly $760 million in assets.

While VIGI devotes almost 24% of its weight to emerging markets stocks, this Vanguard fund is conservatively positioned at the geographic level with Switzerland, Canada and Japan combining for about 40%. That trio also imply a significant runway for dividend growth with this Vanguard income idea.

Vanguard ETFs:  Vanguard International High Dividend Yield ETF (VYMI)

Expense ratio: 0.32%

12-month Yield: 3.2%

Many of the same sentiments applied to the VIG/VIGI relationship are applicable to the Vanguard International High Dividend Yield ETF (NASDAQ:VYMI) and the aforementioned VYM. Like its domestic relative, VYMI does not sport an alarmingly high yield (just 3.2%).

Still, VYMI underscores a couple of important points. First, ex-U.S. dividend payers often sport higher yields than the equivalent U.S. stocks. Second, there is a massive dividend opportunity set outside the U.S. as half or more of the world’s dividend payers are not U.S. stocks.

VYMI holds nearly 900 stocks, over 54% of which are European companies.

Vanguard ETFs: Vanguard Intermediate-Term Corporate Bond ETF (VCIT)

Expense ratio: 0.07%

SEC Yield: 3.3%

Corporate bonds, even investment-grade fare, usually offer higher yields than U.S. Treasuries and the Vanguard Intermediate-Term Corporate Bond ETF (NASDAQ:VCIT) proves as much with a 30-day SEC yield of 3.22%.

VCIT is 91% cheaper than competing funds while offering investors exposure to massive number of investment-grade corporates, 1,752 to be precise. Underscoring this Vanguard ETF’s low credit risk, over 91% of its holdings are rated A or Baa.

As of this writing, Todd Shriber owns shares of VNQ.