diff --git a/Command-Line-Interface.md b/Command-Line-Interface.md
index f96565b..ab1822a 100644
--- a/Command-Line-Interface.md
+++ b/Command-Line-Interface.md
@@ -26,6 +26,10 @@ Commands are:
 * **terminate**: cause the daemon to terminate (may be automatically restarted on some systems)
 * **updatecheck**: check for updates now (if this is an official build with software updates compiled in)
 
+# Join Earth
+
+You can join Earth by running (on Linux and Mac) `sudo zerotier-cli join 8056c2e21c000001`. (Earth is a public virtual network, meaning that it has no access control and allows anyone to join. Make sure your system is up to date and you have no unprotected network services listening.)  See [README.md](https://github.com/zerotier/ZeroTierOne/#zerotier-one---ethernet-virtualization) for more details.
+
 # Authorizing a non-privieged user
 
 On Linux, from the home directory of the user to authorize: