diff --git a/debugger_protocol/_base.py b/debugger_protocol/_base.py
new file mode 100644
index 00000000..f0f8aff9
--- /dev/null
+++ b/debugger_protocol/_base.py
@@ -0,0 +1,28 @@
+
+
+class Readonly(object):
+    """For read-only instances."""
+
+    def __setattr__(self, name, value):
+        raise AttributeError(
+                '{} objects are read-only'.format(type(self).__name__))
+
+    def __delattr__(self, name):
+        raise AttributeError(
+                '{} objects are read-only'.format(type(self).__name__))
+
+    def _bind_attrs(self, **attrs):
+        for name, value in attrs.items():
+            object.__setattr__(self, name, value)
+
+
+class WithRepr(object):
+
+    def _init_args(self):
+        # XXX Extract from __init__()...
+        return ()
+
+    def __repr__(self):
+        args = ', '.join('{}={!r}'.format(arg, value)
+                         for arg, value in self._init_args())
+        return '{}({})'.format(type(self).__name__, args)
diff --git a/debugger_protocol/messages/_base.py b/debugger_protocol/messages/_base.py
new file mode 100644
index 00000000..7efc3e3b
--- /dev/null
+++ b/debugger_protocol/messages/_base.py
@@ -0,0 +1,22 @@
+from debugger_protocol._base import Readonly, WithRepr
+
+
+class Base(Readonly, WithRepr):
+    """Base class for message-related types."""
+
+    _INIT_ARGS = None
+
+    @classmethod
+    def from_data(cls, **kwargs):
+        """Return an instance based on the given raw data."""
+        return cls(**kwargs)
+
+    def __init__(self):
+        self._validate()
+
+    def _validate(self):
+        pass
+
+    def as_data(self):
+        """Return serializable data for the instance."""
+        return {}