Chapter · Master Ethereum
Smart contracts
A smart contract is a small program stored on Ethereum. It holds rules like if this happens, then do that. Once deployed, it runs exactly as written, and no single person can quietly change it. A simple example: a contract that holds funds and only releases them when two people both agree. Nobody needs to trust a middleman, because the code does the job in the open and anyone can inspect it.
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What this lesson covers
Building blocks
Most crypto apps you hear about are really collections of smart contracts working together. A lending app, a token swap, an NFT sale: each is code on Ethereum. This is why people call Ethereum programmable money. In the next lessons we look at how the network actually runs this code and how you pay for it.
What you get asked
What best describes a smart contract?
A smart contract is program code living on Ethereum. When someone triggers it, the network runs the rules exactly as written, with no manual approval step.
Once a smart contract is deployed, its code runs ___, without needing a person to approve each step.
That automation is the point. The rules execute on their own when conditions are met, which removes the need to trust a middleman to act fairly.
Match each smart contract trait to what it means
Openness is the theme. Because the code and its logic are public, users can check the rules before they interact instead of trusting a promise.
Why is a bug in a smart contract a serious problem?
The same trait that makes contracts trustworthy, running exactly as written, means mistakes run too. If a flaw lets funds leak, attackers can drain it fast. Audits reduce this risk but never remove it.
The rest of this chapter
Learn how Ethereum works as a programmable blockchain, from smart contracts and gas to staking, Layer 2s, and DeFi.