diff --git a/api_testgen/core/exceptions.py b/api_testgen/core/exceptions.py
new file mode 100644
index 0000000..5f55cc4
--- /dev/null
+++ b/api_testgen/core/exceptions.py
@@ -0,0 +1,36 @@
+"""Custom exceptions for API TestGen."""
+
+
+class SpecParserError(Exception):
+    """Base exception for spec parser errors."""
+    pass
+
+
+class InvalidOpenAPISpecError(SpecParserError):
+    """Raised when OpenAPI specification is invalid."""
+    pass
+
+
+class UnsupportedVersionError(SpecParserError):
+    """Raised when OpenAPI version is not supported."""
+    pass
+
+
+class AuthConfigError(Exception):
+    """Base exception for auth configuration errors."""
+    pass
+
+
+class MissingSecuritySchemeError(AuthConfigError):
+    """Raised when security scheme is not defined in spec."""
+    pass
+
+
+class GeneratorError(Exception):
+    """Base exception for generator errors."""
+    pass
+
+
+class TemplateRenderError(GeneratorError):
+    """Raised when template rendering fails."""
+    pass