What is financial economics?

Every financial decision comes down to a question of risk. How much uncertainty is worth taking on, and what should it cost? Financial economics is the field built around those questions, giving investors, companies, and regulators a shared framework for thinking through them. Much of that foundation traces back to decades of Nobel-recognized research from economists like Harry Markowitz, Robert Shiller, and Douglas Diamond.

This article explores what financial economics is, the principles behind it, the methods it uses, and how it differs from economics more broadly.

1. Risk and return are linked

The most fundamental principle in financial economics is that higher risk demands higher reward. Investors expect higher returns when they accept more uncertainty. That trade-off underpins portfolio construction, asset pricing, and corporate investment decisions. Without this trade-off, there would be no rational basis for accepting the greater uncertainty of a high-risk investment over the predictable returns of a low-risk one.^{2, 5}

2. Diversification reduces unrewarded risk

Not all risk is worth taking. The risk tied to any single company can be reduced by spreading investments across many of them. What remains is market risk, which moves all assets together. The math behind this is what Markowitz worked out in 1952. A portfolio's volatility depends not only on the volatility of each asset, but also on how the assets move relative to each other.¹

Combining assets that are not perfectly correlated reduces overall volatility without giving up expected return. Markowitz illustrated this in his 1952 paper with a straightforward observation. When one industry struggles, others may not. Therefore, a portfolio spread across different industries is less exposed to any single downturn than one concentrated within a single sector.¹

3. No arbitrage

In a well-functioning market, two assets with identical cash flows must trade at the same price. If they don't, traders will exploit the gap until it closes.⁶ For example, if a stock listed in both New York and London trades at different prices, traders will buy the cheaper one and sell the other until the gap closes.

The Black-Scholes-Merton (BSM) formula made options pricing possible in a rigorous way. Robert Merton and Myron Scholes, working with the late Fischer Black, developed the formula by showing that a risk-free portfolio could be built from a combination of options and shares.⁷

4. Market efficiency

Asset prices tend to reflect new information quickly, which makes it hard to consistently beat the market by analyzing public data.³ William Sharpe built on Markowitz’s portfolio theory to develop the Capital Asset Pricing Model(CAPM), which explains why riskier assets must offer higher expected returns in an efficient market.⁸

Robert Shiller later challenged how far this holds in practice. His research showed that stock prices swing far more than changes in company earnings and dividends can justify, suggesting that markets do not always reflect information accurately.⁹

Financial economics relies on a distinctive set of tools. Some build formal models of uncertainty, while others test whether those models hold up against real market data.

Mathematical modeling

Financial decisions always involve uncertainty about the future. To reason precisely about that uncertainty, economists need a formal language, one that can capture how prices move, how risk compounds, and how different financial instruments relate to each other.

The clearest example is the Black-Scholes-Merton formula for valuing stock options. Merton applied stochastic calculus to model how stock prices and portfolios evolve in continuous time, which allowed him to show that a trading strategy combining options and shares could replicate a risk-free return at every instant.^{6, 7}

Econometrics and empirical testing

Aside from building a method, economists also need to verify whether that theory matches what actually happens in markets. This is what empirical testing does. Lars Peter Hansen developed the Generalized Method of Moments, an econometric method that enables the study of one aspect of a complex model without fully specifying every part of it.¹⁰

This theory transformed empirical research in finance and macroeconomics, allowing economists to test asset pricing models against real data far more rigorously than before.³

Behavioral and experimental approaches

Behavioral and experimental approaches study how people actually make financial decisions, rather than assuming they act with perfect rationality.¹¹ The behavioral side draws on psychology to model how cognitive biases shape financial decision-making¹¹, while the experimental side tests these models by observing how real participants make choices under risk.¹²

Robert Shiller, Daniel Kahneman, and Richard Thaler have used these methods to show that prices often deviate from what classical theory predicts. This work helps explain real-world phenomena like asset bubbles and investor panic, and complements rather than replaces traditional models.⁹

Financial economics is one of the most consequential branches of modern economics because its ideas move real money every day. The work of Nobel-recognized financial economists has given markets, firms, and policymakers the tools to price risk, allocate capital, and absorb shocks.

The field is not a finished project, as new challenges keep the field moving forward. Behavioral finance, financial crises, and digital assets are all areas where financial economists are still developing answers, but the core principles established over decades remain central to how capital markets function.

For insights into financial economics and related fields by Harry Markowitz, William Sharpe, Robert Shiller, and other Nobel laureates, visit Nobel Perspectives & Economic Views.