What Is Money? The Foundation of All Finance

Why Money Exists

Imagine you are a farmer with a surplus of corn. You need shoes, but the shoemaker does not want corn — she wants milk. The milk producer wants firewood. This problem, known as the double coincidence of wants, made direct barter incredibly inefficient for anything beyond the simplest economies.

Early human societies solved this by agreeing on intermediate goods that everyone would accept. Shells, salt, cattle, and eventually metals like gold and silver became commodity money — items with intrinsic value that served as a universal medium of exchange. The word “salary” itself comes from the Latin salarium, referring to payments made in salt.

Over centuries, commodity money evolved into coins stamped by governments, then into paper notes backed by gold reserves (the gold standard), and finally into what we use today: fiat money. The Mexican peso, the US dollar, the euro — none of these are backed by gold or any physical commodity. They have value because governments declare them legal tender and because millions of people trust and accept them in daily transactions.

Understanding this progression matters because it reveals a fundamental truth: money is a social agreement. Its value depends on collective trust, and that trust can strengthen or weaken over time. How this trust is maintained in practice becomes clearer when you understand how banks operate and the institutions behind them.

The Three Functions of Money

Economists describe money through three core functions. Every form of money, from ancient cowrie shells to digital pesos in your bank app, must perform these roles:

Medium of Exchange

This is money’s most visible function. Instead of bartering goods directly, you exchange your labor for money and then exchange that money for the things you need. When you tap your debit card at OXXO or transfer pesos via SPEI, money is acting as a medium of exchange.

For a medium of exchange to work well, it must be widely accepted, easily divisible (you can pay 37.50 pesos, not just round numbers), portable, and durable. Physical peso coins and bills meet these criteria, and digital money improves on portability and speed.

Store of Value

Money allows you to save purchasing power for the future. If you earn 10,000 pesos today, you expect to be able to spend a comparable amount of goods next month or next year. This function is where inflation becomes critically important — if prices rise 10% in a year, your stored 10,000 pesos can buy roughly 10% less. Money that loses value too quickly fails as a store of value, which is exactly what happens during periods of hyperinflation.

Unit of Account

Money provides a common measuring stick for value. A kilogram of tomatoes costs 35 pesos, a movie ticket costs 80 pesos, rent costs 12,000 pesos. Without a shared unit of account, you would need to know the exchange rate between every possible pair of goods — an impossibly complex task. Money simplifies the entire economy into a single numbering system.

What Gives Money Its Value

Since fiat money is not backed by gold, what prevents it from being worthless paper? Several reinforcing factors maintain its value:

Government mandate. The Mexican government declares the peso legal tender. Businesses must accept it for debts, taxes are denominated in pesos, and government contracts are paid in pesos. This creates a baseline of mandatory demand.

Trust and acceptance. Over 130 million people in Mexico use pesos daily. Employers pay wages in pesos, landlords accept rent in pesos, and grocery stores price everything in pesos. This massive network of acceptance is self-reinforcing: you accept pesos because you know others will accept them from you.

Controlled supply. Banxico (Banco de México), the central bank, manages how many pesos circulate in the economy. If too many pesos flood the market, each one becomes worth less — like adding water to a soup. Banxico uses tools like the reference interest rate (tasa de referencia) to influence how much money flows through the economy.

Economic productivity. Ultimately, a currency’s value is anchored to the goods and services the economy produces. A growing, productive economy supports a stronger currency. Economic crises or political instability can undermine confidence and weaken a currency, as Mexico experienced during the 1994 peso crisis.

Inflation: The Silent Tax on Your Money

Inflation is the gradual increase in the general price level of goods and services. When inflation runs at 5% per year, something that costs 100 pesos today will cost approximately 105 pesos a year from now. Your 100-peso bill still says “100” on it, but it buys less.

How Inflation Is Measured

In Mexico, INEGI (the national statistics institute) measures inflation through the INPC (Índice Nacional de Precios al Consumidor), which tracks the prices of a basket of goods and services that a typical household consumes. This includes food, housing, transportation, healthcare, education, and recreation. The percentage change in this index over 12 months gives you the annual inflation rate.

Mexico’s Inflation Context

Mexico has a complicated history with inflation. In the 1980s, inflation exceeded 100% per year, devastating savings and purchasing power. The 1994 peso crisis sent inflation soaring above 50%. These traumatic experiences led to institutional reforms, including granting Banxico constitutional autonomy in 1993 to set monetary policy independently of political pressure.

Today, Banxico targets an inflation rate of 3% (with a tolerance band of plus or minus 1 percentage point). While actual inflation fluctuates — rising above 8% during the post-pandemic period before gradually declining — Mexico’s inflation management is vastly more stable than it was three decades ago.

Why Inflation Matters to You Personally

Inflation is often called a “silent tax” because it reduces your wealth without any explicit charge. Consider these practical effects:

• Savings lose value. If your savings account earns 2% interest but inflation is 5%, you are losing 3% of purchasing power each year. Your balance grows, but what it can buy shrinks.
• Wages may not keep up. If your salary stays flat while prices rise 5%, you received an effective pay cut.
• Fixed debts become cheaper. This is the flip side — if you owe 100,000 pesos at a fixed rate, inflation makes that debt easier to repay in real terms, since future pesos are worth less.

Understanding inflation transforms how you think about financial decisions. It explains why keeping large amounts of cash under your mattress is a guaranteed losing strategy, and why earning a return on your money — even a modest one — is essential.

Banxico: Mexico’s Guardian of the Peso

The Banco de México (Banxico) is one of the most important institutions in your financial life, even if you never interact with it directly. Established in 1925 and granted constitutional autonomy in 1993, Banxico has a primary mandate: maintaining the purchasing power of the Mexican peso.

How Banxico Controls Inflation

Banxico’s main tool is the tasa de referencia (reference interest rate). When inflation rises above the target, Banxico raises this rate. Higher rates make borrowing more expensive, which slows spending and investment, reducing upward pressure on prices. When inflation is under control, Banxico can lower rates to stimulate economic activity.

This mechanism affects you directly. When Banxico raises rates, your credit card interest goes up, mortgage rates increase, but savings accounts and CETES (government bonds) also pay more. When rates drop, borrowing becomes cheaper but savings earn less.

Banxico also manages the money supply through open market operations (buying and selling government bonds) and by setting reserve requirements for banks. The central bank is the sole institution authorized to issue banknotes and coins in Mexico.

The Mexican Peso: A Brief History

The peso has been Mexico’s currency since 1863, though its form has changed dramatically. Before 1993, Mexico used the “old peso,” and by the late 1980s, prices had inflated to absurd levels — a loaf of bread might cost thousands of pesos. In 1993, the government introduced the nuevo peso (new peso), removing three zeros. One new peso equaled 1,000 old pesos. The “nuevo” was eventually dropped, and today we simply use “peso” (MXN).

Current denominations include coins of 10, 20, and 50 centavos, and 1, 2, 5, 10, and 20 pesos. Banknotes come in 20, 50, 100, 200, 500, and 1,000 pesos. The newer polymer (plastic) banknotes are more durable and harder to counterfeit than the older cotton-paper versions.

Digital Money vs. Physical Money

While coins and bills are tangible, the vast majority of pesos exist only as digital entries in bank databases. When your employer deposits your paycheck via SPEI, no physical cash moves — numbers change in computer systems. When you pay with your debit card, the same thing happens.

This distinction matters for several reasons:

• Digital money is traceable. Every SPEI transfer, card payment, and bank transaction leaves a record. This helps prevent fraud but also means the SAT (tax authority) can monitor financial activity.
• Physical cash is anonymous. Cash transactions leave no digital trail, which is why there are legal limits on cash transactions in Mexico (operations above 500,000 pesos in cash must be reported).
• Digital money depends on infrastructure. If the banking system goes down, your digital pesos are temporarily inaccessible. Physical cash works without electricity or internet.
• Both are real money. Whether a peso is a coin in your pocket or a number on your bank app screen, it has identical legal value and purchasing power.

The trend worldwide, and in Mexico specifically, is strongly toward digital payments. SPEI processed billions of transactions in recent years, CoDi (Cobro Digital) enables QR-code payments, and digital-only banks like Nu and Mercado Pago operate entirely without physical branches.

Why Understanding Money Matters

You might wonder why a personal finance course starts with such a theoretical topic. The reason is practical: every financial decision you make is a decision about money, and misunderstanding money leads to costly mistakes.

If you do not understand inflation, you might leave your emergency fund in a zero-interest account, watching it lose value year after year. If you do not understand how Banxico’s rate decisions affect loan costs, you might take on variable-rate debt at the worst possible time. If you do not understand the difference between real and nominal returns, you might think an investment earning 8% is great — until you realize inflation was 7%.

Money is the language of your financial life. The remaining lessons in this module will build on this foundation, showing you how the institutions that manage your money operate and how to navigate the Mexican financial system with confidence.

Key Takeaways

• Money evolved from barter to commodity money to the fiat system we use today, where value comes from government backing and collective trust.
• Money serves three functions: medium of exchange, store of value, and unit of account.
• Inflation erodes purchasing power over time. Mexico targets 3% annual inflation, managed by Banxico.
• Banxico controls inflation primarily through the reference interest rate, which directly affects your borrowing and saving costs.
• The vast majority of money today is digital, and Mexico’s financial infrastructure (SPEI, CoDi) is accelerating this trend.
• Understanding money is not abstract theory — it is the foundation for every financial decision you will make.

In the next lesson, you will learn how banks operate as businesses, how they profit from your deposits, and what fees to watch out for.