In recent years, more and more investors are selecting Exchange Traded Funds (ETFs) over mutual funds. But what exactly is an ETF, and how do they differ from the traditional mutual fund? Modern Portfolio Theory (invented by Nobel laureate Harry Markowitz) states that in order to minimize risk, investors should hold a portfolio of many uncorrelated (unrelated) stocks, similar to the expression “don’t put all of your eggs in one basket.” The problem with MPT is that the average investor would need a lot of money and time to create such a diversified portfolio. Mutual funds and ETFs solve this limitation by allowing investors to gain immediate diversification by combining their funds together.