A mathematical concept developed by Harry Markowitz and modern portfolio theorists in the 1950s which determines a portfolio’s most efficient balance between risk and reward. The efficient frontier is plotted as a curve on a graph and takes into account the standard deviation of the return on all investments with some level of risk over a period of time. The most efficient make-up of a portfolio for the amount of risk will lie on the curve. The overarching take-away for portfolio managers and investors has been to diversify their portfolios.