diff --git a/tests/test_workflow_engine_examples.py b/tests/test_workflow_engine_examples.py
index 375f206..2a6a535 100644
--- a/tests/test_workflow_engine_examples.py
+++ b/tests/test_workflow_engine_examples.py
@@ -16,6 +16,11 @@
 from tests.message_queue import UnitTestMessageQueue
 from tests.wapi_adapter import UnitTestWorkflowAPIAdapter
 from workflow.workflow_engine import WorkflowEngine
+from workflow.workflow_validator import (
+    ValidationLevel,
+    ValidationResult,
+    WorkflowValidator,
+)
 
 
 @pytest.fixture
@@ -55,8 +60,9 @@ def start_workflow(
 
     # To start a workflow we need to:
     # 1. Load and create a Workflow Definition
-    # 2. Create a Running Workflow record
-    # 3. Send a Workflow START message
+    # 2. Validate the workflow for running
+    # 3. Create a Running Workflow record
+    # 4. Send a Workflow START message
     #
     # 1.
     workflow_path = os.path.join(
@@ -68,6 +74,13 @@ def start_workflow(
     wf_response = da.create_workflow(workflow_definition=wf_definition)
     print(f"Created workflow definition {wf_response}")
     # 2.
+    vr_result: ValidationResult = WorkflowValidator.validate(
+        workflow_definition=wf_definition,
+        variables=variables,
+        level=ValidationLevel.RUN,
+    )
+    assert vr_result.error_num == 0
+    # 3.
     response = da.create_running_workflow(
         user_id="dlister",
         workflow_id=wf_response["id"],
diff --git a/workflow/workflow_engine.py b/workflow/workflow_engine.py
index e12ed06..bc7c285 100644
--- a/workflow/workflow_engine.py
+++ b/workflow/workflow_engine.py
@@ -330,22 +330,28 @@ def _validate_step_command(
         # If the returned boolean is False then we can expect the returned str
         # to contain an error message.
         #
-        # Remember that variables can exist in the specification too!
         # The full set of step variables can be obtained
-        # (in descending order of priority) from...
+        # (in ascending order of priority) from...
         #
-        # 1. The RunningWorkflow
-        # 2. The Job Step Specification Variables
+        # 1. The Job Step Specification
+        # 2. The RunningWorkflow
         #
         # If variable 'x' is defined in all three then the RunningWorkflow's
         # value must be used.
 
-        # Get any variables from the step specification.
+        # 1. Get any variables from the step specification.
         all_variables = step_spec.pop("variables") if "variables" in step_spec else {}
-        # Merge running workflow variables on top of these
+        # 2. Merge running workflow variables on top of these
         if running_workflow_variables:
             all_variables |= running_workflow_variables
 
+        # This gives all the running workflow and step-specific variables.
+        # Now we have to inspect the workflow step 'inputs' (and 'options')
+        # and see if there are further variables that need constructing
+        # and then adding (merging) into the 'all_variables' dictionary.
+        #
+        # TBD
+
         message, success = decode(
             job["command"], all_variables, "command", TextEncoding.JINJA2_3_0
         )
diff --git a/workflow/workflow_validator.py b/workflow/workflow_validator.py
index 8040fd2..0ea38cf 100644
--- a/workflow/workflow_validator.py
+++ b/workflow/workflow_validator.py
@@ -5,7 +5,7 @@
 from enum import Enum
 from typing import Any
 
-from .decoder import validate_schema
+from .decoder import get_variable_names, validate_schema
 
 
 class ValidationLevel(Enum):
@@ -39,27 +39,29 @@ def validate(
         *,
         level: ValidationLevel,
         workflow_definition: dict[str, Any],
-        workflow_inputs: dict[str, Any] | None = None,
+        variables: dict[str, Any] | None = None,
     ) -> ValidationResult:
         """Validates the workflow definition (and inputs)
         based on the provided 'level'."""
         assert level in ValidationLevel
         assert isinstance(workflow_definition, dict)
-        if workflow_inputs:
-            assert isinstance(workflow_inputs, dict)
+        if variables:
+            assert isinstance(variables, dict)
 
-        # ALl levels require a schema validation
+        # ALl levels need to pass schema validation
         if error := validate_schema(workflow_definition):
             return ValidationResult(error_num=1, error_msg=[error])
 
+        # Now level-specific validation...
         if level == ValidationLevel.RUN:
             run_level_result: ValidationResult = WorkflowValidator._validate_run_level(
                 workflow_definition=workflow_definition,
-                workflow_inputs=workflow_inputs,
+                variables=variables,
             )
             if run_level_result.error_num:
                 return run_level_result
 
+        # OK if we get here
         return _VALIDATION_SUCCESS
 
     @classmethod
@@ -67,10 +69,9 @@ def _validate_run_level(
         cls,
         *,
         workflow_definition: dict[str, Any],
-        workflow_inputs: dict[str, Any] | None = None,
+        variables: dict[str, Any] | None = None,
     ) -> ValidationResult:
         assert workflow_definition
-        del workflow_inputs
 
         # RUN level requires that each step specification is a valid JSON string.
         # and contains properties for 'collection', 'job', and 'version'.
@@ -104,4 +105,16 @@ def _validate_run_level(
                     error_msg=[f"Specification is missing: {', '.join(missing_keys)}"],
                 )
 
+        # We must have values for all the inputs defined in the workflow.
+        wf_variables: list[str] = get_variable_names(workflow_definition)
+        missing_values: list[str] = []
+        for wf_variable in wf_variables:
+            if not variables or wf_variable not in variables:
+                missing_values.append(wf_variable)
+        if missing_values:
+            return ValidationResult(
+                error_num=3,
+                error_msg=[f"Missing input values for: {', '.join(missing_values)}"],
+            )
+
         return _VALIDATION_SUCCESS