What is Ethereum, and what is a smart contract?
A blockchain that runs programs, not just payments. Smart contracts explained with a vending machine, the DAO hack, the Merge, gas fees, and how Ethereum differs from Bitcoin.
Ethereum is a blockchain that runs programs, not just payments. Bitcoin's ledger records who owns what. Ethereum's ledger also stores small pieces of code called smart contracts, and anyone can trigger them by sending a transaction. That one addition turned a currency idea into a platform, and nearly everything else in crypto, tokens, NFTs, DeFi, most scams too, was built on top of it.
It launched in 2015, proposed by a teenager named Vitalik Buterin who thought Bitcoin's ledger was too limited. Ether, the coin, is the fuel. Every action on the network burns a little of it as a fee, which users call gas.
What is a smart contract?
A program that lives on the blockchain and runs exactly as written, with no company hosting it and no admin able to quietly change it. Think of a vending machine. Put the coin in, get the snack, no cashier involved and no arguing. A smart contract is that, made of code: send this token, receive that one, automatically, every time.
The strength and the danger are the same fact: the code is the contract. If it has a bug, the bug is the contract too. In 2016 a project called The DAO raised about 150 million dollars in ether, someone found a flaw, and drained a third of it without breaking a single rule of the code. Ethereum's community controversially rolled back the chain to undo it, which is why a splinter chain called Ethereum Classic still exists. Audits help. Nothing makes code perfect.
How is Ethereum different from Bitcoin?
Purpose and pace. Bitcoin does one thing, moves value, and changes as slowly as possible on purpose. Ethereum is a construction site that never stops. Its biggest change came in 2022, an upgrade called the Merge, when it dropped energy-hungry mining for proof of stake. Validators now lock up ether as a deposit for the right to confirm blocks, and the network's electricity use fell by more than 99 percent overnight.
Supply differs too. Bitcoin is capped at 21 million forever. Ether has no hard cap, though fees get partially destroyed, which sometimes shrinks the supply. Different philosophies: digital gold on one side, digital infrastructure on the other.
What actually runs on Ethereum?
Tokens, mostly. The standard called ERC-20 lets anyone create a new coin in an afternoon, which gave the world both useful building blocks and an ocean of junk. NFTs live here. Stablecoins like USDC move billions across it daily. DeFi apps, the lending and trading contracts, hold tens of billions in deposits. And every one of those categories has a scam twin, because the same openness that lets a developer deploy a useful contract lets a thief deploy a drainer.
Gas fees are the tax on all of it. When the network is busy, a simple swap can cost more than the coffee you were buying, which is why cheaper networks and Ethereum add-ons called layer 2s keep multiplying.
Is Ethereum a good investment?
Same honest answer as Bitcoin: unknowable, volatile, and nobody's promise. Ether has real usage behind it, which bulls like, and endless competition plus regulatory fog, which bears like. It has crashed more than 80 percent twice and recovered twice. That is a description, not a prediction.
What matters for your safety is narrower. If you use Ethereum apps, every wallet approval you sign is a small legal document written in code. Read what a site asks before clicking approve, keep serious funds in a wallet that never touches experiments, and remember the vending machine: it gives out exactly what the code says, to whoever pressed the button, with no refunds window and no manager to call.