diff --git a/src/ytdl_sub/script/script.py b/src/ytdl_sub/script/script.py
index 5f405ed5..ab18ad6f 100644
--- a/src/ytdl_sub/script/script.py
+++ b/src/ytdl_sub/script/script.py
@@ -8,6 +8,7 @@ from ytdl_sub.script.types.syntax_tree import SyntaxTree
 from ytdl_sub.script.types.variable import Variable
 from ytdl_sub.script.utils.exceptions import UNREACHABLE
 from ytdl_sub.script.utils.exceptions import CycleDetected
+from ytdl_sub.script.utils.exceptions import VariableDoesNotExist
 
 # pylint: disable=missing-raises-doc
 
@@ -38,6 +39,11 @@ class Script:
         deps: List[str],
     ) -> None:
         for dep in variable_dependency.variables:
+            if dep.name not in self._variables:
+                raise VariableDoesNotExist(
+                    f"{variable_name} uses the variable {dep.name} which does not exist."
+                )
+
             if variable_name in deps + [dep.name]:
                 cycle_deps = [variable_name] + deps + [dep.name]
                 cycle_deps_str = " -> ".join(cycle_deps)
diff --git a/src/ytdl_sub/script/utils/exceptions.py b/src/ytdl_sub/script/utils/exceptions.py
index 39f9cb79..b05976d4 100644
--- a/src/ytdl_sub/script/utils/exceptions.py
+++ b/src/ytdl_sub/script/utils/exceptions.py
@@ -19,6 +19,10 @@ class FunctionDoesNotExist(UserException):
     """Tried to use a function that does not exist"""
 
 
+class VariableDoesNotExist(UserException):
+    """Tried to use a variable that does not exist"""
+
+
 class CycleDetected(UserException):
     """A cycle exists within a user's script"""
 
diff --git a/tests/unit/script/types/test_string.py b/tests/unit/script/types/test_string.py
index e9564227..581740c7 100644
--- a/tests/unit/script/types/test_string.py
+++ b/tests/unit/script/types/test_string.py
@@ -5,7 +5,6 @@ import pytest
 from ytdl_sub.script.parser import STRINGS_NOT_CLOSED
 from ytdl_sub.script.parser import STRINGS_ONLY_ARGS
 from ytdl_sub.script.script import Script
-from ytdl_sub.script.types.resolvable import Boolean
 from ytdl_sub.script.types.resolvable import String
 from ytdl_sub.script.utils.exceptions import InvalidSyntaxException
 
diff --git a/tests/unit/script/types/test_variable.py b/tests/unit/script/types/test_variable.py
new file mode 100644
index 00000000..91f47f6c
--- /dev/null
+++ b/tests/unit/script/types/test_variable.py
@@ -0,0 +1,52 @@
+import re
+
+import pytest
+
+from ytdl_sub.script.script import Script
+from ytdl_sub.script.types.resolvable import String
+from ytdl_sub.script.utils.exceptions import CycleDetected
+from ytdl_sub.script.utils.exceptions import VariableDoesNotExist
+
+
+class TestVariable:
+    def test_simple(self):
+        assert Script({"a": "a", "b": "{b_}", "b_": "b"}).resolve() == {
+            "a": String("a"),
+            "b": String("b"),
+            "b_": String("b"),
+        }
+
+    def test_multiple_variables(self):
+        assert Script({"a": "a", "b": "b", "b_": "  {a}  {b}  "}).resolve() == {
+            "a": String("a"),
+            "b": String("b"),
+            "b_": String("  a  b  "),
+        }
+
+    def test_simple_with_function(self):
+        assert Script({"a": "a", "b": "{%capitalize(b_)}", "b_": "b"}).resolve() == {
+            "a": String("a"),
+            "b": String("B"),
+            "b_": String("b"),
+        }
+
+    def test_simple_cycle(self):
+        with pytest.raises(
+            CycleDetected,
+            match=re.escape("Cycle detected within these variables: a -> b -> a"),
+        ):
+            Script({"a": "{b}", "b": "{a}"}).resolve()
+
+    def test_simple_cycle_with_function(self):
+        with pytest.raises(
+            CycleDetected,
+            match=re.escape("Cycle detected within these variables: b -> b_ -> b"),
+        ):
+            Script({"b": "{%capitalize(b_)}", "b_": "{b}"}).resolve()
+
+    def test_undefined_variable(self):
+        with pytest.raises(
+            VariableDoesNotExist,
+            match=re.escape("b uses the variable c which does not exist."),
+        ):
+            Script({"a": "a", "b": "{c}"}).resolve()