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What is mainnet?
Mainnet is a blockchain's main public network, where transactions move coins with real value. It is the opposite of a testnet, which copies the network for testing with coins meant to be worthless.
What it means for you
Anything sent on mainnet costs real fees and cannot be undone, unlike practice transactions on a testnet. Layer 2 networks are separate chains too: tokens on a layer 2 are not on Ethereum mainnet until withdrawn, so check which network an exchange deposit address expects before sending.
How it works
Each network keeps its own state: an address's balance and history on mainnet are separate from the same address on a testnet or a layer 2, and they do not carry over. Since EIP-155, Ethereum transactions include a chain ID in the data that is signed, so a transaction signed for one chain does not work on another; Ethereum mainnet's chain ID is 1. ethereum.org advises against reusing mainnet accounts on testnets for security reasons.
Sources: ethereum.org: Networks, ethereum.org: Layer 2, EIP-155: Simple replay attack protection · checked 4 October 2026
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