Buy small-cap ETF when you already have large-cap of the same market
Yes, you should own a diverse mix of company sizes to be well diversified. While both will probably get hit in a recession, different economies suit different sized companies very differently in many cases, and this diversity positions you best to not only not miss out in cases where small companies do better out of recessions than large, but also in environments where small companies rate of growth is larger in bull markets.
An ETF manager will only allow certain financial organisations to create and redeem ETF shares.  These are called Authorised Participants (APs).  The APs have the resources to bundled up packages of shares that they already own and hold in order to match the ETFs requirements.  In the case of the EDEN ETF, this portfolio is the MSCI Denmark Index.  Only APs transact business directly with the ETF manager.   When ETF shares need to be created, the AP will bundle up the portfolio of shares and deliver them to the ETF manager.  In return, the ETF manager will deliver to the AP the corresponding number of shares in the ETF.  Note that no cash changes hands here. (These ETF shares are now available for trading in the market via the AP.  Note that investors do not transact business directly with the ETF manager.) Similarly, when ETF shares need to be redeemed, the AP will deliver the ETF shares to the ETF manager.  In return, the ETF manager will deliver to the AP the corresponding portfolio of shares.  Again, no cash changes hands here. Normally, with an established and liquid ETF, investors like you and me will transact small purchases and sales of ETF shares with other small investors in the market.  In the event that an AP needs to transact business with an  investor, they will do so by either buying or selling the ETF shares.  In the event that they have insufficient ETF shares to meet demand, they will bundle up a portfolio deliver them to the ETF provider in return for ETF shares, thus enabling them to meet demand.  In the event that a lot of investors are selling and the AP ends up holding an excessive amount of ETF shares, they will deliver unwanted shares to the ETF manager in exchange for a portfolio of the underlying shares. According to this scheme, large liquidations of ETF holdings should not effect the share prices of the underlying portfolio.  This is because the underlying shares are not sold in the market, rather they are simply returned to the AP in exchange for the ETF shares (Recall that no cash is changing hands in this type of transaction).   The corresponding trail of dividends and distributions to ETF share holders follows the same scheme. Depending on your strategy, it could be though there is also something to be said for what kind of order are you placing: Market, limit or otherwise? Something else to consider is whether or not there is some major news that could cause the stock/ETF to gap at the open.  For example, if a company announces strong earnings then it is possible for the stock to open higher than it did the previous day and so a market order may not to take into account that the stock may jump a bit compared to the previous close.  Limit orders can be useful to put a cap on how much you'll pay for a stock though the key would be to factor this into your strategy of when do you buy. Investopedia has this note where you'd want the contrapositive point: The interest rate, commonly bandied about by the media, has a wide and   varied impact upon the economy. When it is raised, the general effect   is a lessening of the amount of money in circulation, which works to   keep inflation low. It also makes borrowing money more expensive,   which affects how consumers and businesses spend their money; this   increases expenses for companies, lowering earnings somewhat for those   with debt to pay. Finally, it tends to make the stock market a   slightly less attractive place to investment. As for evidence, I'd question that anyone could really take out all the other possible economic influences to prove a direct co-relation between the Federal Funds rate and the stock market returns.  For example, of the dozens of indices that are stock related, which ones would you want that evidence: Total market, large-cap, small-cap, value stocks, growth stocks, industrials, tech, utilities, REITs, etc.  This is without considering other possible investment choices such as direct Real Estate holdings, compared to REITs that is, precious metals and collectibles that could also be used. History...  No company has maintained such a high market cap over an extended amount of time.   Not only that, but is Apple worth a trillion dollars?  In a generation will their products be as popular?  They're worth significantly more than Exxon Mobil at this point...  If Apple's market cap does go to a trillion dollars its an upside of 60 percent or so.  Or I can invest in a company like Lenovo whose market cap is 11 billion and is expanding like crazy.  If their valuation goes up even to the 50 billion mark, that's an upside of nearly 400 percent.  Plus there's the whole supply/demand dynamic for a stock that is already widely owned, how much more money can new investors put into it?  When will all the funds who hold massive quantities sell?  Etc...  There are many reasons why no company has maintained a trillion dollar valuation....    Honestly it shocks me that people who frequent a finance message board don't understand these things. Almost all major no-load mutual fund families allow you to do the kind of thing you are talking about, however you may need an initial investment of between $1000 to $3000 depending on the fund.  Once you have it however, annual fee's are usually very little, and the fees to buy that companies funds are usually zero if it's a no-load company (Vanguard, TRowPrice, etc)  With the larger companies that means you have a pretty large selection of funds, but generally EACH fund has a minimum initial purchase, once that's met then you can buy additional amounts in small quantities without a problem. For someone on a smaller budget, many low cost brokers (ETrade as mentioned by Litteadv, Scottrade as mentioned by myself in another similar question today) allow you to start with smaller initial balances and have a small selection of funds or ETF's that you can trade from without commission.  In the case of Scottrade, they have like 15 ETF's that you can trade comission free.  Check with the various low cost brokerages such as ETrade, Scottrade, and TDAmeritrade, to see what their policies are, and what if any funds/ETF's they allow you to trade in without commissions. Keep in mind that for Mutual funds, there may still be a fund minimum initial investment that applies, be sure to check if that is the case or not.  The lack of any minimum investment makes ETF's a slightly more attractive option for someone who doesn't have the 'buy in' that many funds require. The key two things to consider when looking at similar/identical ETFs is the typical (or 'indicative') spread, and the trading volume and size of the ETF. Just like regular stocks, thinly traded ETF's often have quite large spreads between buy and sell: in the 1.5-2%+ range in some cases. This is a huge drain if you make a lot of transactions and can easily be a much larger concern than a relatively trivial difference in ongoing charges depending on your exact expected trading frequency. Poor spreads are also generally related to a lack of liquidity, and illiquid assets are usually the first to become heavily disconnected from the underlying in cases where the authorized participants (APs) face issues. In general with stock ETFs that trade very liquid markets this has historically not been much of an issue, as the creation/redemption mechanism on these types of assets is pretty robust: it's consequences on typical spread is much more important for the average retail investor. On point #3, no, this would create an arbitrage which an authorized participant would quickly take advantage of. Worth reading up about the creation and redemption mechanism (here is a good place to start) to understand the exact way this happens in ETFs as it's very key to how they work. I'm not sure how detailed of an explanation you're hoping for. Bear ETFs basically just short sell the underlying asset. The more highly levered ETFs will also use a combination of options, futures, and swaps to achieve their target leverage. The inversion isn't perfect though, and their target is usually just to close inverse to the *daily* return of their underlying asset.  If you feel like reading, [here is an example.](http://direxioninvestments.onlineprospectus.net/DirexionInvestments//SPXS/index.html?open=Summary%20Prospectus) You can find the investment overview on page 4. "If you are a ""small"" investor (namely, not an accredited investor), then the transaction costs (commissions) for purchasing the stocks while attempting to duplicate DJIA will defeat any benefit. My personal preference is to purchase mutual funds rather than ETFs."