What is DeFi? A Guide from Scratch

DeFi is a complete financial system —savings, loans, currency exchange, investment— that operates without a single employee, without offices, and without any company deciding who gets in. The acronym stands for Decentralized Finance. Instead of a bank that holds your money and approves or denies your transactions, there are computer programs that apply fixed rules automatically: you deposit and the system pays you interest; you request a loan and the system grants it against collateral, without asking who you are. Everything happens on a blockchain (a public database that no one controls alone and that anyone can read), and everything is recorded in plain sight. In this guide, we start from scratch: we explain what a blockchain is, what allows a program to replace a banker, how money is made and lost with a real numerical example, how much money this market moves today, and what risks you assume in exchange for not needing anyone's permission.

What problem does DeFi solve and why does it need a blockchain?

To understand DeFi, it is useful to first look at what a bank does. When you deposit money into an account, the bank safeguards it, keeps track of how much you have, decides the interest rate it pays you, and has the power to freeze your account, reject a transfer, or close your access. All trust rests with that institution: you do not see the ledger; you simply trust that the number appearing in their app is correct.

DeFi changes where that trust lives. Instead of placing it in a company, it places it in open-source code that anyone can read and in a database that no one owns exclusively. It emerged between 2018-2020 on Ethereum, a network designed precisely to execute programs, and grew because it offered something banking did not: access for anyone with an internet connection, without paperwork, without business hours, and without a committee deciding if you deserve an account. The trade-off —as we will see below— is that the protections that same company provided also disappear: deposit insurance, customer service hotlines, and the ability to reverse an error.

That public database that no one owns exclusively has a name: blockchain. Think of a normal banking app. Underneath, there is a database where a company records how much money each client has and logs every movement. If that company wants to change a balance, it can: it is their database and only they write to it.

A blockchain is that same idea —a database that records movements and balances— with one decisive difference: no company controls it. Thousands of independent computers spread across the world keep an identical copy and agree, through mathematical rules, on which version is correct. To add a new movement, it is not enough for someone to write it: the majority of the network must validate it. And once written, it cannot be deleted or rewritten, because that would require falsifying all copies simultaneously.

That property —anyone can read it, no one can manipulate it alone, and what is written is permanent— is what allows for the construction of financial services without a bank at the center. If balances live in a public and unalterable database, you don't need to trust a company to know how much you have: you check it yourself. The analogy has an important limit: that permanence also means an error cannot be undone. If you send funds to the wrong address, no one can reverse it. To go into detail, see our guide on blockchain basics.

What is a smart contract and how does it replace a banker?

Imagine a vending machine. You insert a coin, press a button, and the soda falls out. There is no clerk deciding whether to sell it to you: the rule is hardcoded into the machine and fulfills itself. If you put in the money, you receive the product; if not, nothing falls out. No one can make an exception in your favor or against you.

A smart contract is exactly that, but for financial operations and living inside a blockchain. It is a program that applies rules automatically and predictably: if you deposit tokens, you start earning interest; if your collateral falls below a threshold, your loan is liquidated; if you request an exchange of one token for another, it is executed at the price set by the market at that second. There is no employee to approve, delay, or deny anything. The code is the rule, and the rule is enforced equally for everyone —with the consequence that there is also no one to call to ask for an exception: you cannot convince a vending machine to give you a soda on credit, and you cannot ask a protocol for an extension if your loan is about to be liquidated.

Here another term appears that is worth defining: a token is a unit of value that lives on a blockchain. It can represent a digital currency, a dollar (stablecoins, tokens designed to always be worth one dollar), a stake in a protocol, or almost anything. When you deposit "tokens" in DeFi, you are moving those units from one smart contract to another.

The strength of this model is predictability: the rules are public and applied without discrimination. Its limit is just as clear: if the program has a bug in its code, that bug will also execute without anyone stopping it. We delve deeper into this in what is a smart contract.

What services does DeFi offer exactly?

DeFi rebuilds almost all the financial services you already know, plus some that didn't exist before. These are the main categories:

For a detailed explanation of each service, consult our complete guide to DeFi.

How is money made in DeFi and how is it seen on the blockchain?

The simplest way to earn is to lend. A concrete and verifiable example is useful. Suppose you deposit the equivalent of $1,000 in USDC —a stablecoin always worth one dollar— into Aave. The protocol lends your dollars to other users who provide collateral above what they borrow, and pays you with the interest they provide.

If the USDC deposit rate is, say, 4% annually, after one year you will have earned about $40 —$1,040 in total— without having done anything other than depositing. If the rate were 6%, it would be $60 (rates vary daily based on demand; on the Ethereum mainnet they usually hover around 3-4%). The difference from a bank is twofold: the rate adjusts itself based on how many people are borrowing at any given time, and every movement is recorded on the blockchain. You can open a public explorer, paste the Aave contract address, and check for yourself how much has been lent, at what rate, and how much has been paid to you. There is no statement you have to take on faith: the raw data is there.

Beyond simple lending, money is made by collecting fees for providing liquidity to a decentralized exchange, earning rewards for staking, or depositing in vaults that reinvest interest so it generates more interest. In all cases, the principle is the same: your capital works within a smart contract and the reward arrives automatically. And in all cases, a high yield is always a sign of higher risk, not a free opportunity.

How does DeFi differ from a traditional bank?

The services feel familiar. The underlying infrastructure is radically different. This table translates each banking product to its DeFi equivalent and highlights the fundamental change:

The last row summarizes the central tension: the absence of an intermediary is the advantage and, at the same time, the absence of a safety net. For a broader comparison, including regulatory differences, see crypto vs traditional banking.

What do you need to use DeFi: wallet and gas?

In banking, your account is your identity. In DeFi, your account is your wallet. A wallet is an application that stores the cryptographic keys that prove those tokens are yours. It works like the key to your house: whoever has the key has access. Therefore, if you lose the key, there is no recovery service to return it to you; and if someone steals it, they can empty your account. The two most used are MetaMask (for Ethereum and compatible networks like Arbitrum, Polygon, Base, or Optimism) and Phantom (for Solana). More detail in what is a wallet.

When you connect your wallet to a protocol, you give it permission to interact with your tokens —but the protocol cannot move anything without your explicit approval for each transaction. The control is yours, and so is the responsibility.

Every action on a blockchain —sending, swapping, depositing— costs a small fee called gas, which you pay to the computers that process your transaction. It is the equivalent of a processing stamp, except here it doesn't go to a company but to the network that keeps the system running. The cost depends on the network: on the Ethereum mainnet, it can range from a few to several dozen dollars per transaction; on "Layer 2" networks like Arbitrum, Base, or Optimism, it drops to cents; on Solana, it is usually a fraction of a cent. This is one of the reasons why much of DeFi activity has moved to these cheaper networks. We expand on this in what is gas.

How much money does DeFi move and how much is lost in hacks?

This is the area where it is useful to look at concrete and dated figures, because they change quickly. The standard metric for measuring the size of DeFi is TVL (Total Value Locked: the total value deposited in all protocols at once).

The honest reading of these numbers is twofold. On one hand, DeFi moves hundreds of billions of dollars sustainably: it is not a marginal experiment. On the other hand, losses from thefts and scams are counted in the billions every year: in 2025, nearly $3.4 billion was stolen in crypto according to the Chainalysis annual report —including the $1.5 billion theft from Bybit in February, attributed to the North Korean group Lazarus—; other firms like TRM Labs, with a different methodology, place it around $2.87 billion. These figures are live and should be checked at a source like DefiLlama or Chainalysis reports before use. To contextualize the size with more nuance, see our guide on what is TVL.

What are the real advantages and risks of DeFi?

The advantages explain why DeFi has attracted so much capital:

• Open access. Anyone with internet and a wallet can participate. No nationality requirement, no minimum balance, no waiting for account approval.
• Transparency. Every transaction, every interest rate, and every line of code is public. You can verify everything yourself on the blockchain.
• Composability. Protocols fit together like pieces: you can stake ETH, use the resulting token as collateral for a loan, and put the borrowed amount into a vault, all in the same afternoon.
• No gatekeepers. As long as you control your wallet, no one can deny you service, change the conditions on their own, or freeze your funds.
• Always open. It operates 365 days a year, with no market hours.

The risks are just as real, and there is no one behind them to cushion the blow:

• Code failures. A smart contract can have bugs. Even audited protocols have been exploited, and deposited funds can be lost permanently.
• No safety net. There is no deposit insurance, no customer service, and no fraud department. If you use the wrong address or fall for a fake website, there is no one to call.
• Irreversible transactions. What is written on the blockchain cannot be undone. An error is permanent.
• Exit scams (rug pulls). Since anyone can deploy a smart contract, scammers can too: they launch a project, attract deposits, and disappear with the money. This is called a rug pull.
• Complexity and regulatory uncertainty. Understanding fees, token approvals, price slippage, and collateral levels takes time; and legal rules change by country and over time.

To manage all this, read how to understand risk in DeFi and how to stay safe.

How to keep track of everything you have in DeFi?

To the previous risks, a less dramatic but very real one is added: the difficulty of not losing sight of what you have. The openness of DeFi is its greatest virtue and, at the same time, its greatest practical inconvenience. A regular user can end up with tokens spread across three or four different networks, positions in eight or ten protocols, a mix of loans, staking, liquidity, and vaults, and dozens of tokens —some of which are merely "receipts" representing positions elsewhere. Knowing what you have, what you owe, what you are earning, and what risks you are exposed to becomes genuinely difficult. Most end up with a spreadsheet, half a dozen tabs open in the browser, and the suspicion of having forgotten something.

Where to start understanding DeFi?

In summary: a blockchain is a public and unalterable database, a smart contract applies rules like a vending machine, a wallet is your account, and gas is the fee for each transaction. From here, the next step is to choose a branch and go deeper:

Sources and links: Ethereum.org (what is DeFi) · DefiLlama (TVL and stablecoins) · Aave (lending protocol) · Chainalysis — crypto thefts 2025 · TRM Labs — crypto crime report 2026