diff --git a/cli/src/m2_market/ledger.py b/cli/src/m2_market/ledger.py
new file mode 100644
index 0000000..d49d549
--- /dev/null
+++ b/cli/src/m2_market/ledger.py
@@ -0,0 +1,96 @@
+"""HTTP client for the m2-ledger service (contracts/ledger-api.md)."""
+
+from __future__ import annotations
+
+import httpx
+
+DEFAULT_TIMEOUT = 10.0
+
+
+class LedgerError(Exception):
+    """Any ledger error not covered by a more specific exception."""
+
+    def __init__(self, message: str, status_code: int | None = None, body: dict | None = None):
+        super().__init__(message)
+        self.status_code = status_code
+        self.body = body or {}
+
+
+class InsufficientFunds(LedgerError):
+    """Raised on 402 — insufficient balance, nothing written."""
+
+
+class DuplicateRef(LedgerError):
+    """Raised on 409 — same ref already settled/refunded (idempotency guard)."""
+
+
+class LedgerClient:
+    def __init__(self, base_url: str, api_key: str, timeout: float = DEFAULT_TIMEOUT):
+        self._client = httpx.Client(
+            base_url=base_url,
+            headers={"X-API-Key": api_key},
+            timeout=timeout,
+        )
+
+    def close(self) -> None:
+        self._client.close()
+
+    def __enter__(self) -> "LedgerClient":
+        return self
+
+    def __exit__(self, *exc_info) -> None:
+        self.close()
+
+    def _raise_for_error(self, response: httpx.Response) -> None:
+        try:
+            body = response.json()
+        except ValueError:
+            body = {}
+        message = body.get("error", response.text)
+        if response.status_code == 402:
+            raise InsufficientFunds(message, response.status_code, body)
+        if response.status_code == 409:
+            raise DuplicateRef(message, response.status_code, body)
+        raise LedgerError(message, response.status_code, body)
+
+    def balance(self, operator_id: str) -> dict:
+        response = self._client.get(f"/balance/{operator_id}")
+        if response.status_code != 200:
+            self._raise_for_error(response)
+        return response.json()
+
+    def install(
+        self,
+        buyer: str,
+        seller: str,
+        amount: int,
+        ref: str,
+        platform_pct: float | None = None,
+    ) -> dict:
+        body = {"buyer": buyer, "seller": seller, "amount": amount, "ref": ref}
+        if platform_pct is not None:
+            body["platform_pct"] = platform_pct
+        response = self._client.post("/tx/install", json=body)
+        if response.status_code != 200:
+            self._raise_for_error(response)
+        return response.json()["grant"]
+
+    def refund(self, ref: str) -> list:
+        response = self._client.post("/tx/refund", json={"ref": ref})
+        if response.status_code != 200:
+            self._raise_for_error(response)
+        return response.json()["tx_ids"]
+
+    def transactions(self, **filters) -> list:
+        response = self._client.get("/tx", params=filters)
+        if response.status_code != 200:
+            self._raise_for_error(response)
+        return response.json()["transactions"]
+
+    def license(self, operator_id: str, listing_id: str) -> dict | None:
+        response = self._client.get(f"/license/{operator_id}/{listing_id}")
+        if response.status_code == 404:
+            return None
+        if response.status_code != 200:
+            self._raise_for_error(response)
+        return response.json()["grant"]