A bridge is a tool that lets you move digital assets from one blockchain to another. Different blockchains, such as Ethereum, Solana, BNB Chain, and Avalanche, are separate networks that cannot communicate with each other by default. A bridge solves that problem by creating a connection between two chains so that your tokens can travel across them.
You can imagine it as changing currency at an international airport. You may go with US dollars, but local shops only accept euros. The exchange booth converts your dollars into euros so you can spend them where you are. A crypto bridge does something similar; it takes your token on one blockchain and makes an equivalent version of it available on another. The actual token does not “move”; it gets locked on the source chain while a corresponding one is minted on the destination chain to represent it. Bridging back reverses the process, causing your new token to burn and your original to unlock.
For example, suppose you own ETH on the mainnet but wish to use a DeFi app on Arbitrum, a Layer 2 faster and cheaper network built on top of Ethereum. You can directly connect your wallet to the official Arbitrum Bridge or a third-party bridge like Stargate Finance, select an ETH amount, approve, and soon thereafter have your ETH available on Arbitrum. The centralized exchange is not involved in the whole process.
Not every bridge is constructed in the same way. There are custodial options, meaning a company or group holds your locked tokens and you trust them to follow through. Some of them are decentralized such that smart contracts (i.e., self-executing code on the blockchain) lock and mint automatically without a middleman. While decentralized bridges mitigate counterparty risk, they are still vulnerable to code exploits. Bridge hacks are actually amongst the most damaging hacks in crypto history. In 2022, the Ronin Bridge hack resulted in a whopping theft of over $600 million in assets, making it one of the largest hacks ever.
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Recognizing the importance of bridges is essential, as the cryptocurrency ecosystem is more than a single network, it comprises many separate chains that have their own strengths, communities, and applications. People often think the situation is connected through the bridge. If not for gateways, all your coins would be stuck on whatever original chain they are on, and the vision of a truly open and interoperable financial system would fall apart. Whether you want to use DeFi, Layer 2 networks, or multichain applications, you will see bridges early. Prior to confirming any transaction, you should always make sure you are on an official or highly audited bridge and check the destination chain.