1  The Economic Role of Banks

1.1 Overview

1.1.1 Learning Objectives

By the end of this chapter, you should be able to:

  1. Explain the fundamental economic problem that banks solve
  2. Describe how banks create value on both sides of the balance sheet
  3. Understand the trade-off between value creation and fragility in banking
  4. Explain why maturity transformation is both socially valuable and inherently risky

1.1.2 Roadmap

What Is a Bank?

  • Stylized balance sheet
  • Functions of banking

Value Creation: The Asset Side

  • Monitoring and screening borrowers
  • Delegated monitoring

Value Creation: The Liability Side

  • Creating money-like deposits
  • Liquidity insurance and liquidity creation

The Central Tension

  • Maturity transformation: value vs. fragility
  • The two sides of banking

1.2 What Is a Bank?

1.2.1 A Boring Definition

NoteDefinition: Bank

A bank is a financial institution that intermediates funds between savers and borrowers.

This definition, while accurate, doesn’t tell us much about:

  • Why banks are useful
  • How they create value
  • What makes them special

To understand these questions, we need to look at what banks actually do.

1.2.2 The Stylized Bank Balance Sheet

Banks perform valuable activities on both sides of their balance sheet:

Assets (Uses of Funds)

  • Loans to borrowers
  • Securities (bonds, treasuries)
  • Cash reserves

Liabilities (Sources of Funds)

  • Deposits (money-like claims)
  • Equity capital
BANK BALANCE SHEET
ASSETS
LIABILITIES
Loans
Securities
Deposits
Capital
TipKey Insight (Doug Diamond)

Banks create value through their activities on both sides of the balance sheet, not just one.

1.3 Value Creation: The Asset Side

1.3.1 Monitoring and Screening Borrowers

Banks specialize in evaluating creditworthiness and monitoring loan performance.

Why is this valuable?

  1. Information production: Banks invest in acquiring information about borrowers

    • Credit history
    • Business fundamentals
    • Character and reputation

  2. Economies of scale: Fixed costs of monitoring spread over many loans

  3. Expertise: Banks develop specialized knowledge about industries and credit risk

ImportantThe Delegated Monitoring Problem

Individual savers lack the expertise, scale, and incentives to monitor borrowers effectively. Banks solve this by delegating the monitoring function to a specialized intermediary.

1.4 Value Creation: The Liability Side

1.4.1 Creating Money-Like Deposits

Banks offer deposit accounts that function as a medium of exchange and store of value.

Key features of deposits:

  1. Redeemable on demand at par: You can withdraw $100 any time and get exactly $100

  2. Accepted for payments: Deposits can be transferred to pay for goods and services

  3. Stable value: Unlike equity or bonds, deposits don’t fluctuate in nominal value

NoteWhy Is This Valuable?

Depositors value:

  • Liquidity: Ability to access funds when needed
  • Safety: Predictable nominal value
  • Convenience: Easy to use for transactions

Banks create these features by transforming illiquid loans into liquid deposits.

ImportantLiquidity Insurance and Liquidity Creation

Individual savers face uncertain liquidity needs but cannot efficiently self-insure. Banks solve this by pooling liquidity risk across many depositors and providing liquidity insurance — offering liquid deposits backed by illiquid assets. This is liquidity creation: banks create more liquidity than exists in the underlying assets.

1.4.2 The Social Value of Banks

Everything we’ve described so far — monitoring borrowers, creating liquid deposits — generates real social value:

  • Borrowers get funding they couldn’t access directly from savers
  • Savers get safe, liquid claims backed by productive investments
  • The economy channels savings into productive projects more efficiently

How? Through maturity transformation:

  • Assets: Long-term, illiquid loans (e.g., 30-year mortgages)
  • Liabilities: Short-term, liquid deposits (redeemable on demand)
NoteBut there is a catch

The very feature that makes deposits valuable — redeemable on demand — means the bank must always be ready to pay out. Yet its assets are locked up in long-term loans. This mismatch is the source of banking’s fragility.

1.5 The Central Tension: Value vs. Fragility

Maturity transformation is how banks create value. It is also how they become fragile.

The value it creates

  • Savers get liquidity
  • Borrowers get long-term funding
  • Banks earn the spread

Example: - Bank makes 10-year mortgage at 6% - Funds with deposits paying 2% - Spread = 4%

The fragility it creates

  • Assets are locked in long-term loans
  • Deposits are redeemable any time
  • If too many depositors withdraw at once, the bank cannot pay

The worst case: - Bank must sell illiquid assets at fire-sale prices - Losses can wipe out equity - Bank fails

ImportantCentral Question

Maturity transformation is socially valuable but inherently fragile. Why do banks engage in it? What problem are they solving that makes the risk worthwhile?

NoteThe Two Sides of Banking

Banks create value on both sides of the balance sheet: - Asset side: Delegated monitoring of borrowers - Liability side: Liquidity creation and insurance

We begin with the liability side — how banks create liquidity and provide insurance against uncertain liquidity needs. This is the Diamond-Dybvig model.

We then examine the fragility this creates (bank runs), before turning to the asset side to study delegated monitoring in detail.