Why lending exists at all
Before we talk about DeFi, let's remember what lending is. Someone has capital they're not using. Someone else has a productive use for that capital but no access to it. A contract transfers the capital, specifies a return schedule, and — most importantly — specifies what happens when the return doesn't arrive. Traditional finance solved this with a tall stack of institutions: banks, credit bureaus, courts, collection agencies. DeFi rebuilt the stack using one tool: collateral that the protocol itself can seize without asking anyone.
That single change — the collapse of the enforcement layer into code — is why DeFi lending exists as a category and why it behaves differently from every form of credit that came before it.
The three primitives
Every lending protocol you'll encounter — Aave, Compound, Maker, Morpho, Spark, Silo, Fraxlend — is some combination of three building blocks: a pool, an interest-rate curve, and a liquidation engine. The pool aggregates supplier capital and lets borrowers draw against it. The curve turns utilization (how much of the pool is borrowed) into an interest rate; when utilization climbs, rates spike to attract more supply or repel borrowers. The liquidation engine watches every position's health factor and auctions off collateral the moment it dips below a threshold.
Understand these three pieces and you can read any DeFi lending protocol in about ten minutes. Everything else — governance tokens, isolated markets, eMode, flash loans — is a layer on top.
Major protocols at a glance
Aave is the reference implementation: multi-asset pools, variable and stable rates, isolation mode for long-tail assets. Compound is the minimalist ancestor — the simplest curve, the cleanest codebase, the most audited. Maker (now Sky) is the odd one out: you don't borrow from a pool, you mint DAI against collateral, which makes DAI itself an obligation of the protocol rather than a liability of a supplier. Morpho layers a peer-to-peer matching engine on top of Aave and Compound, trying to close the spread between lend and borrow rates. Frax, Silo, Euler, Radiant, Spark each carve a niche: stablecoin-native, isolated-pool, cross-chain, LST-focused.
You don't need to memorize them. You need to know that they all make the same three decisions — pool shape, rate curve, liquidation mechanics — and their differences come down to how aggressively they tune each dial.
The risks nobody emails you about
Smart contract risk is obvious and mostly priced in by now. Oracle risk — the price feed that the liquidation engine relies on — is less talked about and historically the cause of most large DeFi blowups. Governance risk is a slow-burning one: a protocol can change its parameters between the block you supply and the block you withdraw. And then there's the composability risk of DeFi itself, where a cascade in one pool drains adjacent ones through liquidation spirals.
If you walk away with one thing, let it be this: DeFi lending has destroyed any illusion that credit is a safe asset class. The assets that back the loans are volatile, the protocols that enforce the loans are software, and the safety nets that protect you in TradFi simply don't exist here. Treat it accordingly.