What Is Ethereum?

Ethereum is a blockchain that runs programs, not just payments. Where Bitcoin's ledger records who owns which coins, Ethereum's ledger also stores code — smart contracts — that executes automatically when triggered, letting people build exchanges, lending markets, and entirely new kinds of applications directly on the chain. Its currency, ether (ETH), is both an asset people hold and the fuel that pays for every computation the network performs.

From calculator to computer

Bitcoin proved a network of strangers could maintain a shared ledger with no operator. Its scripting abilities, though, are deliberately minimal — roughly a calculator bolted onto a vault. In late 2013, a 19-year-old programmer named Vitalik Buterin proposed generalizing the idea: instead of a blockchain that supports one application (money), build one that supports any application developers can code. Ethereum launched in July 2015 after a public crowdsale, built by Buterin and a group of co-founders.

The generalization is the whole innovation. Every Ethereum node runs the Ethereum Virtual Machine (EVM), a shared computing environment. Deploy a program to it and that program lives at an address on the chain, visible to everyone, executing exactly as written, for anyone who calls it — with no server, no company hosting it, and no one able to take it down or quietly alter it. People summarize this as a "world computer": slow and expensive per operation compared to any laptop, but neutral, always on, and shared by everyone.

Smart contracts: vending machines, not lawyers

The name "smart contract" misleads; nothing legal is involved. A smart contract is simply a program on the blockchain that holds funds and follows rules. The classic analogy is a vending machine: insert the right coins, make a selection, and the machine dispenses — no clerk, no discretion, no trust required. The machine is the agreement.

A concrete example: a simple escrow contract could hold a buyer's 1 ETH and release it to the seller only when both parties confirm delivery, refunding automatically after 30 days otherwise. Once deployed, neither party can change the rules or grab the funds early; the code enforces the deal.

Scale that primitive up and you get Ethereum's application landscape:

• Token standards. Anyone can issue a token with a short contract. Most stablecoins (dollar-tracking tokens, covered later in this path) live on Ethereum this way, as do thousands of project tokens.
• Decentralized exchanges. Contracts that hold pools of two tokens and let anyone trade against them at algorithmically set prices — an exchange with no company operating it.
• Lending markets. Contracts where users deposit assets to earn interest and borrow against collateral, with liquidations enforced by code rather than a risk desk.
• NFTs, naming systems, games, DAOs — organizations whose treasuries and voting rules are themselves contracts.

The honest caveat: "the code enforces the deal" means bugs are enforced too. Smart-contract exploits have drained protocols of hundreds of millions of dollars at a time, and a contract's immutability means a discovered flaw often can't be patched in place. On Ethereum, trust in institutions is replaced by trust in code — an upgrade only when the code deserves it.

ETH, gas, and why fees exist

Every operation on Ethereum — a transfer, a swap, deploying a contract — consumes computation on thousands of machines at once, so every operation costs a fee, paid in ETH and called gas. Simple transfers are cheap in gas terms; complex contract interactions cost more. Fees float with demand: when the network is quiet a swap might cost well under a dollar, and in peak congestion the same swap has historically cost tens of dollars. (The fees guide later in this path covers tactics; layered networks built on top of Ethereum now handle much activity at much lower cost.)

Gas isn't just a toll — it's a security mechanism. Because every step of computation must be paid for, no one can freeze the world computer with an infinite loop or spam it for free.

ETH therefore differs from BTC in kind, not just in brand: BTC is designed to be held and transferred; ETH is used — it's the metering unit of a compute platform, staked to secure the network, and burned in part with every transaction (since a 2021 upgrade, a portion of each fee is destroyed, linking network usage to ETH's supply). Ethereum has no fixed supply cap like Bitcoin's 21 million; instead it has low, rule-based issuance to validators, offset by that fee burning.

The Merge and proof of stake

Ethereum launched using proof-of-work mining, like Bitcoin. In September 2022 it executed the Merge: a live switch of its entire security model to proof of stake, where validators lock up 32 ETH each as collateral and are penalized ("slashed") for cheating, replacing energy expenditure with capital at risk. The switch cut the network's energy consumption by roughly 99.9% and stands as one of the more remarkable feats in software history — comparable to swapping an airliner's engines mid-flight, with hundreds of billions of dollars aboard.

The practical consequences for a beginner:

• Staking yield exists. ETH holders can earn protocol rewards by staking, directly or through services — with real risks attached, covered in the DeFi path.
• Energy criticism largely doesn't apply. Post-Merge Ethereum's footprint is that of a modest server fleet, not a country.
• Different trust profile than Bitcoin. Proof of stake is more intricate, younger, and concentrates influence with large ETH holders; Bitcoiners consider proof of work's physical cost the more battle-tested anchor. Reasonable people disagree, and both models have now run for years without a consensus failure.

Ethereum vs Bitcoin: different jobs

Beginners often frame the two as competitors. Mostly they aren't — they're optimized for different jobs:

	Bitcoin	Ethereum
Launched	2009	2015
Core purpose	Scarce monetary asset	Programmable application platform
Native coin	BTC — held, transferred	ETH — fuel, stake, and asset
Supply	Hard cap: 21 million	No cap; low issuance, partly offset by fee burning
Consensus	Proof of work	Proof of stake (since 2022)
Protocol changes	Rare and conservative	Regular, roadmap-driven upgrades

The philosophical split is real: Bitcoin treats ossification — changing as little as possible — as a feature, because money benefits from predictability. Ethereum treats evolution as a feature, because a platform competes on capability. Each choice is coherent; each carries its own risk (stagnation versus upgrade missteps). Owning one is a bet on scarce digital money; owning the other is closer to a bet on a decentralized computing platform and the economy built on top of it. Everything in this site's DeFi path runs, directly or by descent, on the machinery this guide just described.

Key Takeaways

• Ethereum, launched in 2015 from Vitalik Buterin's proposal, generalized Bitcoin's breakthrough: a blockchain that runs arbitrary programs, not just a payments ledger.
• Smart contracts are vending machines in code — they hold funds and execute rules automatically, enabling exchanges, lending markets, and tokens with no operating company; bugs, however, are enforced as faithfully as features.
• ETH is the network's fuel: every operation costs gas, which secures the platform against spam and makes ETH a used asset, not just a held one.
• The 2022 Merge moved Ethereum to proof of stake, cutting energy use by roughly 99.9% and enabling staking, at the cost of a younger, more complex security model.
• Bitcoin and Ethereum do different jobs — conservative scarce money versus an evolving application platform — and most of crypto beyond payments builds on Ethereum's model.