ETF Size: Micro-Cap ETFs are exchange-traded funds that trade on stock exchanges, just like stocks. They are a basket of securities, meaning they hold a group of assets. ETFs offer exposure to a diversified group of assets in a single investment. This makes them appealing to investors who want to easily add exposure to new asset classes or indexes. Micro-Cap ETFs offer exposure to the smallest companies by market capitalization. These companies have a market cap of $300 million or less. ETFs that track micro-cap stocks tend to be very volatile and risky. They also tend to have higher expense ratios than ETFs that track large-cap stocks. For these reasons, Micro-Cap ETFs are not for everyone. But for investors who are comfortable with risk and willing to pay higher fees, they can offer the potential for high returns.