A blockchain is a distributed database that stores records in linked, cryptographically-secured blocks — making data nearly impossible to alter retroactively. It's the technology behind Bitcoin, Ethereum, Polymarket, and nearly every major DeFi protocol.
Imagine a notebook that thousands of people hold identical copies of. Whenever someone writes a new entry, it's broadcast to everyone, verified, and added to all copies simultaneously. To alter a past entry, you'd need to change everyone's notebook at once — an impossible task. That's blockchain in concept.
Technically, a blockchain is an append-only data structure where each block contains:
The hash of each block is computed from the block's contents — so if you change any transaction in a block, its hash changes, breaking the chain from that point forward. This cryptographic linking makes the history tamper-evident.
With no central authority, how do thousands of distributed nodes agree on which transactions are valid? Through consensus mechanisms — the rules that determine which version of the ledger is "correct."
Miners race to find a number (the nonce) that, when hashed with the block data, produces an output below a difficulty target. This is computationally expensive by design. The first miner to solve it broadcasts the block, receives the block reward, and all nodes add it to their chain. Changing history requires redoing all this work — a 51% attack — which is economically infeasible for Bitcoin given its mining hashrate.
Validators stake (lock up) cryptocurrency as collateral. The network pseudorandomly selects validators to propose and attest to blocks, weighted by their stake. Misbehaviour (e.g., signing conflicting blocks) results in slashing — a portion of their stake is destroyed. PoS uses ~99.95% less energy than PoW, which is why Ethereum switched ("The Merge") in 2022.
| Feature | Proof of Work | Proof of Stake |
|---|---|---|
| Security model | Computational cost | Economic stake at risk |
| Energy use | Very high | Very low |
| Major chains | Bitcoin, Litecoin | Ethereum, Solana, Polygon |
| Attack cost | Buy hardware + electricity | Buy 33%+ of staked coins |
A cryptographic hash function converts any input into a fixed-length output. Bitcoin uses SHA-256. Key properties:
Every blockchain wallet uses public-key cryptography. You have a private key (like a password — never share it) and a public key (like an account number — safe to share). When you send a transaction, you sign it with your private key, proving ownership without revealing the key itself. Anyone can verify the signature using your public key.
Polymarket is built on the Polygon blockchain. Every trade you make is a signed transaction broadcast to the Polygon network, verified by validators, and recorded immutably. The resolution of each market is handled by a smart contract — automated, transparent, and not controlled by any single entity.
A smart contract is code that lives on a blockchain and executes automatically when predefined conditions are met. No intermediary needed. Polymarket's YES/NO market resolution, DeFi loan liquidations, and NFT royalties all run on smart contracts.
Most blockchain guides focus on Bitcoin or DeFi yields — but for prediction market traders, understanding the specific blockchain Polymarket uses (Polygon) is directly useful. Polygon is an Ethereum-compatible Layer 2 network: transactions cost under $0.01, settle in ~2 seconds, and are fully verifiable on PolygonScan. This matters because every Polymarket trade, every market resolution, and every USDC balance is on-chain — you can audit it independently without trusting the Polymarket interface.
The UMA oracle that resolves Polymarket markets also operates via smart contracts: the resolution bond, the 2-hour dispute window, and the UMA token holder vote are all blockchain-enforced. A disputed market can't be quietly resolved against traders by a company decision — the resolution logic is publicly readable code. This is the structural advantage of DeFi prediction markets over traditional bookmakers that no centralised platform can match.