diff --git a/README.md b/README.md
index 77c9100..3f7c93c 100644
--- a/README.md
+++ b/README.md
@@ -30,7 +30,22 @@ Arc is an open EVM-compatible layer 1 built on [Malachite](https://github.com/ci
 - 🚀 **[Execution](crates/node/README.md)** - Execution binary and configuration
 - 🗳️ **[Consensus](crates/malachite-app/README.md)** - Consensus binary and configuration
 - More: see Arc [developer docs](https://docs.arc.io/arc/concepts/welcome-to-arc) for guides, APIs, and specs
+## USDC units and decimals
 
+Arc exposes USDC as both the native token and through an ERC-20 interface. These
+interfaces use different decimal representations:
+
+- The ERC-20 USDC interface uses **6 decimals**.
+- Native balance and native-value accounting use **18-decimal units**.
+- Converting an ERC-20 USDC amount to native units multiplies the amount by
+  `10^12`.
+
+For example, 1 USDC is represented as `1_000_000` through the ERC-20 interface
+and as `1_000_000_000_000_000_000` in native units.
+
+When integrating with Arc, applications should use the decimal representation
+expected by the interface they are interacting with rather than assuming the
+same unit scale for both representations.
 ## Install and Run a Node
 
 ### Install