diff --git a/src/fr24sdk/__init__.py b/src/fr24sdk/__init__.py
index 9bd0b1c..ef2de58 100644
--- a/src/fr24sdk/__init__.py
+++ b/src/fr24sdk/__init__.py
@@ -13,6 +13,7 @@
     TransportError,
     ApiError,
     AuthenticationError,
+    NoApiKeyError,
     RateLimitError,
     PaymentRequiredError,
     BadRequestError,
@@ -26,6 +27,7 @@
     "TransportError",
     "ApiError",
     "AuthenticationError",
+    "NoApiKeyError",
     "RateLimitError",
     "PaymentRequiredError",
     "BadRequestError",
diff --git a/src/fr24sdk/exceptions.py b/src/fr24sdk/exceptions.py
index 98e0c99..76d66a9 100644
--- a/src/fr24sdk/exceptions.py
+++ b/src/fr24sdk/exceptions.py
@@ -66,6 +66,21 @@ class AuthenticationError(ApiError):
     pass
 
 
+class NoApiKeyError(Fr24SdkError):
+    """Indicates that no API key was provided for authentication.
+    
+    This is a specific type of authentication error that occurs when the SDK
+    is used without providing an API token, either through the constructor
+    or the FR24_API_TOKEN environment variable.
+    
+    Unlike other ApiError subclasses, this error is raised before any HTTP
+    request is made, so it doesn't include request/response context.
+    """
+
+    def __init__(self, message: str):
+        super().__init__(message)
+
+
 class RateLimitError(ApiError):
     """Indicates that the API rate limit has been exceeded (402 Payment Required or 429 Too Many Requests)."""
 
diff --git a/src/fr24sdk/transport.py b/src/fr24sdk/transport.py
index ef31727..72bab1f 100644
--- a/src/fr24sdk/transport.py
+++ b/src/fr24sdk/transport.py
@@ -12,6 +12,7 @@
 from .exceptions import (
     ApiError,
     AuthenticationError,
+    NoApiKeyError,
     RateLimitError,
     TransportError,
     PaymentRequiredError,
@@ -73,6 +74,14 @@ def request(
     ) -> httpx.Response:
         """Makes an HTTP request to the API."""
 
+        # Check if API token is available before making the request
+        if not self.api_token:
+            raise NoApiKeyError(
+                "No API key provided. Please set the FR24_API_TOKEN environment variable "
+                "or pass an api_token parameter when creating the Client. "
+                "For more information, see https://fr24api.flightradar24.com/docs"
+            )
+
         request_headers = self._get_default_headers()
         if headers:
             request_headers.update(headers)
diff --git a/uv.lock b/uv.lock
index 9fe854a..943b4ce 100644
--- a/uv.lock
+++ b/uv.lock
@@ -606,7 +606,7 @@ wheels = [
 
 [[package]]
 name = "fr24sdk"
-version = "0.0.1"
+version = "0.1.0"
 source = { editable = "." }
 dependencies = [
     { name = "exceptiongroup", marker = "python_full_version < '3.11'" },