What is Portfolio?

An investment portfolio is the total suite of financial assets held by an individual, investment firm, or institution. This collection typically spans a wide range of asset classes, including stocks, bonds, cash, exchange-traded funds (ETFs), mutual funds, and real estate, but can also include alternative investments such as commodities, private equity, or venture capital. Rather than viewing each investment in isolation, portfolio management evaluates the collection as a cohesive unit designed to achieve the owner's long-term financial goals.

The construction and management of a portfolio are heavily guided by Modern Portfolio Theory (MPT), which focuses on maximizing expected return for a given level of risk through diversification. By selecting assets that are not perfectly correlated, investors can lower their exposure to single-stock or sector-specific volatility. A critical component of portfolio maintenance is asset allocation, defining the percentage of the portfolio dedicated to each asset class based on the investor's risk tolerance, financial goals, and time horizon.

Over time, market movements will naturally cause the portfolio's assets to drift from their original weights. To prevent this drift from exposing the investor to unwanted risk, they must periodically engage in rebalancing, which involves selling overperforming assets and buying underperforming ones to restore the target asset allocation.