# Chains & Networks

### Overview 

Different blockchains have different rules and tools. You must know what chain you are on to send assets, pay fees, and interact with apps.

### Core concepts

* Block: Batch of transactions added to the chain.
* Consensus: How the network agrees on the next block.
* Layer 1 (L1): Base networks (e.g., Ethereum, Mosaic).
* Layer 2 (L2): Scales an L1 by processing off-chain/rollups.
* Parachain: A network connected to a relay chain (Polkadot).
* Substrate: Framework for building Polkadot-style chains.
* EVM: Ethereum Virtual Machine; runs Solidity smart contracts.

### Key takeaways

* Apps are chain-specific; pick the right network in your wallet.
* Mosaic supports Substrate and EVM so projects and users can choose what fits.
* Fees are paid in the chain’s native token.

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