Investing in the foreign currency market, more commonly known as forex trading, used to be off-limits to many retail investors. Until recently, forex trading was reserved for professionals at big investment banks, hedge funds and central banks.

But today, any investor who wants to can participate in the forex market. Of course, that does not mean forex trading is for everyone.To be sure, there are compelling reasons to consider forex as an investment option. First, the market is open 24 hours a day, 7 days a week, enabling you to trade when the Asian markets open if you are so inclined. Second, forex brokers offer a considerable amount of leverage, meaning you can open an account with just several hundred dollars and have the ability to trade a much larger sum of money. Third, the forex market is the most liquid financial market in the world. Every day more money changes hands in this market than all of the world's equity and bond markets combined.

But this truly is a trader's market and not every investor is a trader. Fortunately, there is a way to get your forex fix without being chained to a computer. ETFs are the best way for investors to gain exposure to a variety of currencies without having to deal with the everyday volatility of the forex market. Let's have a look at some of the important forex ETFs investors should know about.

PowerShares DB US Dollar Index Bullish ETF (NYSE: UUP)

In the forex world, the dollar still rules the roost. That makes UUP a must-know among currency ETFs, since it mirrors the dollar's performance. UUP is one of the most liquid currency ETFs on the market with average daily trading volume of over 4.7 million shares. This is an important consideration because many currency ETFs are thinly traded, even some that track major currencies.

UUP tracks the U.S. Dollar Index, measuring the dollar's strength against the euro, the British pound, the Japanese yen, the Canadian dollar, the Swedish krona and the Swiss franc. Investors should also be aware of UUP's bearish equivalent, the PowerShares DB US Dollar Index Bearish ETF (NYSE: UDN), if a short dollar position is more appropriate.

CurrencyShares Euor Trust (NYSE: FXE)

The euro, used by 16 European nations including economic giants France and Germany, is the second most heavily traded currency following the U.S. dollar. The euro is viewed as a riskier asset than either the dollar or yen, so when the market's appetite for risk is high, the euro generally outperforms other major currencies.

The opposite holds true as well: investors flee more volatile currencies when risk appetite wanes. Fortunately, FXE has a popular bearish counterpart that should also be on your list of currency ETFs: The ProShares Ultra Short Euro ETF (NYSE: EUO).

Wisdom Tree Dreyfus Emerging Currency ETF (NYSE: CEW)

Investing in emerging market equities can be tricky, but trading emerging market currencies can be downright dangerous. It's probably better for most investors to get exposure through an emerging currency ETF like CEW. CEW invests in some currencies that could be considered conservative emerging market plays, like the Brazilian real, Chinese yuan and Indian rupee. But CEW's other constituents, including Chile, Hungary, Israel, Malaysia and Mexico, make this an ETF worth a look for those willing to add substantial risk to their portfolios.

PowerShares DB G10 Currency Harvest ETF (NYSE: DBV)

DBV focuses exclusively on developed market currencies. DBV is comprised of futures contracts in 10 different currencies, including the euro, yen, Australian dollar, Canadian dollar, pound, franc and Norwegian krone. note that DBV does not measure the strength of the U.S. Dollar relative to its other holdings. Rather, the Dollar is in the basket of 10 currencies tracked by DBV.

CurrencyShares Australian Dollar Trust (NYSE: FXA)

The Australian dollar is known as a commodity currency, meaning its value has a strong correlation to the price of commodities – in this case gold. History has shown that when gold prices move higher, the Aussie dollar usually follows in step. That means investors can indirectly gain exposure to gold by owning FXA. Another reason to consider FXA is the general willingness of the Reserve Bank of Australia to raise interest rates – good news for investors holding Australian dollars.

CurrencyShares Canadian Dollar Trust (NYSE: FXC)

The Canadian dollar is another commodity currency. Also knowns as the loonie, the Canadian dollar has a historical correlation to crude oil prices because Canada is one of the largest crude producers in the world. In fact, the Canadian oil sands region is believed to hold one of the largest oil reserves outside the Middle East. Oil has a significant impact on Canada's economy and, in turn, on the value of the loonie. Consider FXC as a backdoor play on oil prices, especially as oil companies may be looking to move operations from the Gulf of Mexico as offshore drilling becomes more regulated.