DeFi, short for wallet.">decentralized finance, is a set of financial services that run on public blockchains instead of banks and brokers. Lending, borrowing, trading and staking are handled by smart contracts: programs that anyone can use with a wallet, at any hour, without opening an account. This guide explains DeFi for beginners and intermediate users: how lending, decentralized exchanges and liquid staking work, where yields really come from, the main risks, and how to start safely.
You will need a self-custody wallet and a basic understanding of stablecoins. If needed, read crypto wallets explained and what are stablecoins first.
What is DeFi, in simple terms?
In traditional finance, a bank holds your money, decides who can borrow, and keeps the ledger. In DeFi, those roles are played by code deployed on a blockchain such as Ethereum, its layer 2 networks, or Solana:
- Your assets stay in your wallet until you deposit them into a protocol.
- The rules (interest rates, collateral, fees) are written in the smart contract and visible to everyone.
- Anyone can use the service; there is usually no identity check at the protocol level.
- Transactions are final. There is no customer service to reverse a mistake.
This openness is the strength of DeFi and the source of most of its risks.
The main DeFi services
Lending and borrowing
Lending protocols pool deposits from lenders and let borrowers take loans against collateral. Aave, the largest of them, is a good example.
- Lenders deposit assets such as USDC or ETH and earn interest paid by borrowers.
- Borrowers must lock more collateral than they borrow (over-collateralisation). Deposit $1,000 of ETH and you might borrow a few hundred dollars of stablecoins.
- If the collateral value falls below a threshold, the position is liquidated: part of the collateral is sold automatically, with a penalty.
- Interest rates are set by algorithm and rise when a pool is heavily used.
Aave continues to evolve: according to Aave Labs, Aave V4, built on a new “hub-and-spoke” design, was activated on Ethereum mainnet on 30 March 2026, alongside the existing V3 markets.
Decentralized exchanges (DEXs)
A decentralized exchange lets you swap one token for another directly from your wallet. Most DEXs, including Uniswap, use liquidity pools instead of an order book:
- Liquidity providers deposit two tokens into a pool and receive a share of the trading fees.
- A formula sets the price according to the ratio of tokens in the pool. Large trades in small pools move the price (slippage).
- Providers are exposed to impermanent loss: when prices move, they can end up with less value than if they had simply held the tokens.
Uniswap v4, deployed at the end of January 2025, keeps all pools in a single contract and adds “hooks”, plug-ins that let developers customise how a pool behaves.
Liquid staking
Proof-of-stake networks reward users who lock tokens to secure them. On Ethereum, running a validator requires 32 ETH and technical work. Liquid staking protocols such as Lido accept any amount, stake it through professional node operators, and give you a token in return (stETH for Lido) that represents your staked ETH plus rewards.
The advantage is that this token stays usable: you can sell it, lend it or use it as collateral. Lido V3, live on Ethereum mainnet since 30 January 2026, added “stVaults”, configurable staking vaults for institutions and developers built on stETH.
Other building blocks
- Stablecoins, the cash of DeFi, used in most loans and trades.
- Bridges, which move tokens between blockchains and have historically been a frequent target of hacks.
- Yield aggregators and vaults, which automate strategies across several protocols.
- Derivatives and perpetual futures exchanges, for advanced users.
A worked example: borrowing against ETH
Here is what a simple loan looks like, with round, illustrative numbers (each market sets its own parameters):
- You deposit 1 ETH worth $3,000 as collateral in a lending market.
- The market lets you borrow up to a set share of that value. You choose to borrow only $1,000 of USDC, well below the maximum.
- The protocol tracks a “health factor” that compares your collateral, adjusted by a liquidation threshold, with your debt. Above 1, you are safe.
- If ETH falls sharply, the health factor drops. Below 1, liquidators can repay part of your debt and take some of your ETH at a discount.
- To close the position, you repay the USDC plus interest and withdraw your ETH.
The lesson: the less you borrow relative to your collateral, the more price drop you can survive. Many losses in DeFi come not from hacks but from loans taken too close to the limit during a volatile market.
Where do DeFi yields come from?
A yield is never free. Before depositing, ask where the money comes from:
| Source of yield | Who pays | Main risk |
|---|---|---|
| Lending interest | Borrowers | Bad debt if liquidations fail, smart contract bugs |
| Trading fees | Traders on a DEX | Impermanent loss, low volume |
| Staking rewards | The blockchain protocol | Slashing, depeg of the liquid staking token |
| Token incentives | The protocol, by issuing new tokens | Falling token price, rewards that stop |
| Leverage and looping | Your own borrowed funds | Liquidation, rate changes |
If a protocol cannot clearly explain where its yield comes from, or if the yield is far above what lending, fees and staking produce elsewhere, treat it as a warning sign.
The risks of DeFi
Smart contract bugs and hacks
A bug in the code can let an attacker drain a protocol, even after several audits. In May 2025, an attacker exploited a math flaw in Cetus, a DEX on Sui, and took about $223 million; Sui validators froze roughly $162 million of it. In November 2025, a rounding flaw in some Balancer V2 pools was exploited across several networks: Balancer’s post-mortem estimated user losses at about $95 million, and outside trackers cited higher totals.
Oracle failures
DeFi protocols read prices from oracles. If an oracle is slow, wrong or manipulated, loans can be liquidated unfairly, or an attacker can borrow against inflated collateral. In October 2022, an attacker manipulated the price of the MNGO token to drain about $110 million from Mango Markets.
Depegs
A token supposed to track a dollar or ETH can lose its peg. In November 2025, Stream Finance disclosed a loss of about $93 million by an external fund manager; its xUSD token fell by more than 70% within a day, and the shock spread to lending markets that accepted it as collateral. Liquid staking tokens can also trade below ETH when many holders sell at once, as stETH did in June 2022.
Other risks
- Governance and admin keys: a team or a small group of token holders can often change parameters or upgrade contracts.
- Front-ends: a hijacked website can serve malicious transactions even if the contracts are safe.
- Phishing and wallet drainers, the most common way individual users lose funds.
- Regulation: fully decentralised protocols fall outside MiCA, so there is no licence, no complaints procedure and no compensation scheme.
How to start with DeFi safely
- Learn with small amounts you can afford to lose entirely.
- Use a hardware wallet, and a separate “hot” wallet with limited funds for new applications.
- Reach protocols only through bookmarked official URLs, never through ads or messages.
- Prefer established protocols with a long track record, public audits and a bug bounty.
- Read what each transaction does before signing, and limit token approvals to the amount needed.
- Keep a safety margin on any loan: monitor your health factor and avoid borrowing close to the limit.
- Diversify across protocols and keep records of every transaction for taxes.
- Revoke old approvals regularly and stay informed about incidents.
The ethereum.org introduction to DeFi and the official docs of each protocol are good places to continue.
Key takeaways
DeFi replaces intermediaries with open code: you gain access, transparency and control, but you take on technical risks that a bank would normally absorb. Understand where each yield comes from, start small, and never deposit more than you are prepared to lose.
