diff --git a/kalshi_client/constants.py b/kalshi_client/constants.py
new file mode 100644
index 00000000..73c05ced
--- /dev/null
+++ b/kalshi_client/constants.py
@@ -0,0 +1,11 @@
+"""
+Shared constants used across the Kalshi client.
+"""
+
+ENV_DEMO = "demo"
+ENV_PROD = "prod"
+
+SUPPORTED_ENVIRONMENTS = {
+    ENV_DEMO,
+    ENV_PROD,
+}