What is a stablecoin?

The concept

A stablecoin is a crypto asset engineered to hold a stable value, almost always pegged 1:1 to a fiat currency like the US dollar, by backing the token with one of three things: fiat reserves, crypto collateral, or an algorithmic/synthetic supply mechanism. The word "stable" is doing real work here — Bitcoin and Ether can move 10% in a day, which is fine for a speculative asset but useless for a merchant who needs to know that $100 received today is still worth $100 tomorrow when rent is due.

Stablecoins exist to solve that mismatch. They let traders move in and out of volatile positions without leaving the blockchain (parking value in USDC between trades instead of cashing out to a bank, which is slow). They let DeFi protocols denominate loans, collateral and interest in a unit that doesn't itself introduce volatility risk into the loan. And they let merchants and remittance apps accept blockchain-based payments without pricing everything in a currency that could swing wildly between invoice and settlement.

Three families dominate the space, and this course spends a full module on each:

1. Fiat-backed — a regulated issuer holds cash and cash-equivalents (short-dated Treasuries, bank deposits) equal to the tokens in circulation, and redeems tokens for fiat on demand. USDC and USDT are the largest examples.
2. Crypto-backed — the token is minted against an over-collateralized basket of volatile crypto assets locked in a smart contract, with no fiat reserve at all. DAI is the standard example.
3. Synthetic / algorithmic — the peg is maintained through a derivative hedge (a spot asset offset by a short futures position) or through algorithmic mint/burn arbitrage rather than a 1:1 reserve. Ethena's USDe and the collapsed Terra UST are the two examples this course returns to repeatedly, because they show both the promise and the failure mode of this family.

Scale matters here too: as of this course's writing, stablecoins collectively represent well over $150 billion in circulating value, with USDT and USDC alone accounting for the large majority of that figure, and stablecoin transfer volume on public blockchains regularly exceeds the combined settlement volume of major card networks on a given day. That scale is precisely why regulators (Module 4) and risk teams at exchanges, custodians and payment companies care so much about getting the mechanics right — a stablecoin is no longer a niche crypto-native tool, it is increasingly plumbing for global payments.

Every stablecoin, regardless of family, is answering the same question for its holder: "If I want my dollar back, what exactly stands behind my claim, and how fast can I get it?" That question — reserve composition, redemption mechanism, and redemption speed — is the thread that runs through this entire course, from reserve attestation (Module 1) to issuance and redemption flows (Module 2) to regulatory reserve requirements (Module 4) to what happens when the answer turns out to be "less than you thought" (Module 5, depeg case studies).

Worked example

Trace a single dollar's journey into a fiat-backed stablecoin:

Day 0:  Institutional client wires $1,000,000 to Circle's reserve bank account.
Day 0:  Circle's operations team confirms the wire has landed and matches it
        to the client's account in their ledger.
Day 0:  Circle's Minter role calls mint(clientWalletAddress, 1_000_000e6)
        on the USDC smart contract (USDC uses 6 decimals).
Day 0:  1,000,000 USDC appears in the client's whitelisted Ethereum wallet,
        usable immediately in any USDC-compatible application.
Month-end: Circle's independent accountant (Grant Thornton) issues an
        attestation confirming that reserves held that day were >= total
        USDC in circulation, including this client's $1,000,000.

Nothing exotic happens here — it's a wire transfer followed by a database write (the mint) on a public ledger instead of a private one. The entire rest of this course is really an exploration of what can go wrong around the edges of this simple flow: slow redemptions, opaque reserves, broken pegs, and unclear regulation. Compare that to a crypto-backed mint, where there is no wire transfer at all — a user simply locks ETH into a smart contract and the contract itself issues the stablecoin debt, with the "reserve" being the on-chain collateral rather than a bank balance. You'll walk through that flow in detail in Lesson 1.3.

Exercise

List three products or workflows where a volatile asset like ETH would break the user experience, and explain in two or three sentences each why a stablecoin solves it. Use at least one example from each of these categories:

• A cross-border remittance app
• A DeFi lending or borrowing protocol
• A merchant checkout or point-of-sale system

For each one, be specific about what breaks without a stable unit of account (e.g., "a lender can't price a 30-day loan in ETH because the collateral value itself might move 20% before the loan matures") rather than just asserting "volatility is bad." Then add a fourth, harder note: pick one of your three examples and identify which stablecoin family (fiat-backed, crypto-backed, or synthetic) would be the worst fit for it, and explain the specific mismatch — for instance, a merchant accepting payments may be uncomfortable with a crypto-backed stablecoin's dependence on a liquidation mechanism they can't audit in real time. Submit your notes before moving to Lesson 1.2, where you'll see how the first family — fiat-backed stablecoins — actually implements the reserve side of this promise.

Recap

• A stablecoin holds a stable peg (usually to the US dollar) via fiat reserves, crypto collateral, or an algorithmic/synthetic mechanism.
• The question "what backs my claim, and how fast can I redeem it?" differs by family and is the throughline of this entire course.
• You now have a map of the three families — fiat-backed, crypto-backed, synthetic — that Modules 1 through 5 will each dissect in depth, at a scale (well over $150B in circulation) that makes these mechanics load-bearing for real payment infrastructure.

Resources

• Circle — What is USDC: https://www.circle.com/en/usdc
• Bank for International Settlements — working papers on stablecoins and payments: https://www.bis.org/topic/fintech.htm
• Financial Stability Board — High-level recommendations for the regulation of crypto-asset activities: https://www.fsb.org/work-of-the-fsb/financial-innovation-and-structural-change/crypto-assets-and-global-stablecoins/