diff --git a/docs/overview.mdx b/docs/overview.mdx
index e5bdcb3..8834a6c 100644
--- a/docs/overview.mdx
+++ b/docs/overview.mdx
@@ -27,3 +27,11 @@ These are the RPC endpoints you can use in your applications to interact with th
 **Mainnet**: https://mainnet.fuel.network/v1/graphql
 
 > Note that this is the same endpoint used in the playground above.
+
+## Chain Id
+
+A chain ID is a unique identifier assigned to a blockchain network, whether a testnet or a mainnet (Fuel Ignition), to ensure correct transaction signing and prevent replay attacks across chains.
+
+**Testnet**: [`0`](https://github.com/FuelLabs/chain-configuration/blob/master/ignition-test/chain_config.json#L41)
+
+**Mainnet**: [`9889`](https://github.com/FuelLabs/chain-configuration/blob/master/ignition/chain_config.json#L41)