diff --git a/class_wrapper.h b/class_wrapper.h
index dbb64e4a..4fedde09 100644
--- a/class_wrapper.h
+++ b/class_wrapper.h
@@ -65,7 +65,38 @@ class ClassWrapper
     template <class MemberType>
     void def_read_write(MemberType T::*pm, const char* name)
         { m_class->def_read_write(pm, name); }
- private:
+        
+    // declare the given class a base class of this and register 
+    // conversion functions
+    template <class S, class V>
+    void declare_base(ClassWrapper<S, V> const & base)
+    {
+        m_class->declare_base(base.m_class.get());
+    }
+
+    // declare the given class a base class of this and register 
+    // conversion functions
+    template <class S, class V>
+    void declare_base(ClassWrapper<S, V> const & base, WithoutDowncast)
+    {
+        m_class->declare_base(base.m_class.get(), without_downcast);
+    }
+
+    template <class S, class V>
+    void declare_base(ExtensionClass<S, V> * base)
+    {
+        m_class->declare_base(base);
+    }
+        
+    // declare the given class a base class of this and register 
+    // only upcast function
+    template <class S, class V>
+    void declare_base(ExtensionClass<S, V> * base, WithoutDowncast)
+    {
+        m_class->declare_base(base, without_downcast);
+    }
+    
+// private:
     PyPtr<ExtensionClass<T, U> > m_class;
 };
 
diff --git a/extclass.cpp b/extclass.cpp
index a1734760..a4f723ae 100644
--- a/extclass.cpp
+++ b/extclass.cpp
@@ -157,7 +157,7 @@ void report_missing_instance_data(
     }
     else    
     {
-        two_string_error(PyExc_TypeError, "extension class '%.*s' is not derived from '%.*s'.",
+        two_string_error(PyExc_TypeError, "extension class '%.*s' is not convertible into '%.*s'.",
                          instance->ob_type->tp_name, target_class->tp_name);
     }
 }
@@ -218,6 +218,41 @@ ExtensionClassBase::ExtensionClassBase(const char* name)
 {
 }
 
+void * ExtensionClassBase::try_class_conversions(InstanceHolderBase * object) const
+{
+    void * result = try_sub_class_conversions(object);
+    if(result) return result;
+    result = try_super_class_conversions(object);
+    return result;
+}
+
+void * ExtensionClassBase::try_super_class_conversions(InstanceHolderBase * object) const
+{
+    void * result = 0;
+    for(int i=0; i<base_classes().size(); ++i)
+    {
+        if(base_classes()[i].second == 0) continue;
+        result = base_classes()[i].first->convert_from_holder(object);
+        if(result) return (*base_classes()[i].second)(result);
+        result = base_classes()[i].first->try_super_class_conversions(object);
+        if(result) return (*base_classes()[i].second)(result);
+    }
+    return 0;
+}
+
+void * ExtensionClassBase::try_sub_class_conversions(InstanceHolderBase * object) const
+{
+    void * result = 0;
+    for(int i=0; i<sub_classes().size(); ++i)
+    {
+        result = sub_classes()[i].first->convert_from_holder(object);
+        if(result) return (*sub_classes()[i].second)(result);
+        result = sub_classes()[i].first->try_sub_class_conversions(object);
+        if(result) return (*sub_classes()[i].second)(result);
+    }
+    return 0;
+}
+
 void ExtensionClassBase::add_method(Function* method, const char* name)
 {
     add_method(PyPtr<Function>(method), name);
diff --git a/extclass.h b/extclass.h
index 3374c0ae..fb96955d 100644
--- a/extclass.h
+++ b/extclass.h
@@ -52,6 +52,9 @@ T* check_non_null(T* p)
 }
 
 template <class T> class HeldInstance;
+typedef void * (*ConversionFct)(void *);
+typedef std::pair<TypeObjectBase *, ConversionFct> BaseClassInfo;
+typedef std::pair<TypeObjectBase *, ConversionFct> SubClassInfo;
 
 class ExtensionClassBase : public Class<ExtensionInstance>
 {
@@ -66,18 +69,30 @@ class ExtensionClassBase : public Class<ExtensionInstance>
     void add_constructor_object(Function*);
     void add_setter_method(Function*, const char* name);
     void add_getter_method(Function*, const char* name);
+    
+    virtual void * try_class_conversions(InstanceHolderBase*) const;
+    virtual void * try_super_class_conversions(InstanceHolderBase*) const;
+    virtual void * try_sub_class_conversions(InstanceHolderBase*) const;
+    virtual std::vector<BaseClassInfo> const & base_classes() const = 0;
+    virtual std::vector<SubClassInfo> const & sub_classes() const = 0;
 };
 
 template <class T>
 class ClassRegistry
 {
- public:
+ public:    
     static Class<ExtensionInstance>* class_object()
         { return static_class_object; }
     static void register_class(py::Class<py::ExtensionInstance>*);
     static void unregister_class(py::Class<py::ExtensionInstance>*);
+    static void register_base_class(BaseClassInfo const &);
+    static void register_sub_class(SubClassInfo const &);
+    static std::vector<BaseClassInfo> const & base_classes();
+    static std::vector<SubClassInfo> const & sub_classes();
  private:
     static py::Class<py::ExtensionInstance>* static_class_object;
+    static std::vector<BaseClassInfo> static_base_class_info;
+    static std::vector<SubClassInfo> static_sub_class_info;
 };
 
 #ifdef PY_NO_INLINE_FRIENDS_IN_NAMESPACE // back to global namespace for this GCC bug
@@ -123,6 +138,10 @@ class PyExtensionClassConverters
             py::InstanceHolder<T>* held = dynamic_cast<py::InstanceHolder<T>*>(*p);
             if (held != 0)
                 return held->target();
+
+            void * target = py::ClassRegistry<T>::class_object()->try_class_conversions(*p);
+            if(target) 
+                return static_cast<T *>(target);
         }
         py::report_missing_instance_data(self, py::ClassRegistry<T>::class_object(), typeid(T));
         throw py::ArgumentError();
@@ -250,6 +269,23 @@ class ReadOnlySetattrFunction : public Function
     String m_name;
 };
 
+template <class From, class To>
+struct ConversionFunction
+{
+    static void * upcast_ptr(void * v)
+    {
+        return static_cast<To *>(static_cast<From *>(v));
+    }
+
+    static void * downcast_ptr(void * v)
+    {
+        return dynamic_cast<To *>(static_cast<From *>(v));
+    }
+};
+
+enum WithoutDowncast { without_downcast };
+
+
 // An easy way to make an extension base class which wraps T. Note that Python
 // subclasses of this class will simply be Class<ExtensionInstance> objects.
 //
@@ -344,10 +380,40 @@ class ExtensionClass
         this->def_getter(pm, name);
         this->def_setter(pm, name);
     }
+        
+    // declare the given class a base class of this and register 
+    // conversion functions
+    template <class S, class V>
+    void declare_base(ExtensionClass<S, V> * base)
+    {
+        BaseClassInfo baseInfo(base, &ConversionFunction<S, T>::downcast_ptr);
+        ClassRegistry<T>::register_base_class(baseInfo);
+        add_base(Ptr(as_object(base)));
+        
+        SubClassInfo subInfo(this, &ConversionFunction<T, S>::upcast_ptr);
+        ClassRegistry<S>::register_sub_class(subInfo);
+    }
+        
+    // declare the given class a base class of this and register 
+    // only upcast function
+    template <class S, class V>
+    void declare_base(ExtensionClass<S, V> * base, WithoutDowncast)
+    {
+        BaseClassInfo baseInfo(base, 0);
+        ClassRegistry<T>::register_base_class(baseInfo);
+        add_base(Ptr(as_object(base)));
+        
+        SubClassInfo subInfo(this, &ConversionFunction<T, S>::upcast_ptr);
+        ClassRegistry<S>::register_sub_class(subInfo);
+    }
     
  private:
     typedef InstanceValueHolder<T,U> Holder;
     
+    virtual std::vector<BaseClassInfo> const & base_classes() const;
+    virtual std::vector<SubClassInfo> const & sub_classes() const;
+    virtual void * convert_from_holder(InstanceHolderBase * v) const;
+
     template <class Signature>
     void add_constructor(Signature sig)
     {
@@ -464,6 +530,28 @@ ExtensionClass<T, U>::ExtensionClass(const char* name)
     ClassRegistry<T>::register_class(this);
 }
 
+template <class T, class U>
+inline
+std::vector<BaseClassInfo> const & ExtensionClass<T, U>::base_classes() const
+{
+    return ClassRegistry<T>::base_classes();
+}
+
+template <class T, class U>
+inline
+std::vector<SubClassInfo> const & ExtensionClass<T, U>::sub_classes() const
+{
+    return ClassRegistry<T>::sub_classes();
+}
+       
+template <class T, class U>
+void * ExtensionClass<T, U>::convert_from_holder(InstanceHolderBase * v) const
+{
+    py::InstanceHolder<T>* held = dynamic_cast<py::InstanceHolder<T>*>(v);
+    if(held) return held->target();
+    return 0;
+}
+
 template <class T, class U>
 ExtensionClass<T, U>::~ExtensionClass()
 {
@@ -487,11 +575,39 @@ inline void ClassRegistry<T>::unregister_class(Class<ExtensionInstance>* p)
     static_class_object = 0;
 }
 
+template <class T>
+void ClassRegistry<T>::register_base_class(BaseClassInfo const & i)
+{
+    static_base_class_info.push_back(i);
+}
+
+template <class T>
+void ClassRegistry<T>::register_sub_class(SubClassInfo const & i)
+{
+    static_sub_class_info.push_back(i);
+}
+
+template <class T>
+std::vector<BaseClassInfo> const & ClassRegistry<T>::base_classes()
+{
+    return static_base_class_info;
+}
+
+template <class T>
+std::vector<SubClassInfo> const & ClassRegistry<T>::sub_classes()
+{
+    return static_sub_class_info;
+}
+
 //
 // Static data member declaration.
 //
 template <class T>
 Class<py::ExtensionInstance>* ClassRegistry<T>::static_class_object;
+template <class T>
+std::vector<BaseClassInfo> ClassRegistry<T>::static_base_class_info;
+template <class T>
+std::vector<SubClassInfo> ClassRegistry<T>::static_sub_class_info;
 
 } // namespace py
 
diff --git a/extclass_demo.cpp b/extclass_demo.cpp
index 7b678120..6ea54f5e 100644
--- a/extclass_demo.cpp
+++ b/extclass_demo.cpp
@@ -363,6 +363,68 @@ static int getX(OverloadTest * u)
     return u->x();
 }
 
+
+/************************************************************/
+/*                                                          */
+/*    classes to test base declarations snd conversions     */
+/*                                                          */
+/************************************************************/
+
+struct Dummy
+{
+    int dummy_;
+};
+
+struct Base
+{
+    virtual int x() const { return 999; };
+};
+
+// inherit Dummy so that the Base part of Concrete starts at an offset
+// otherwise, typecast tests wouldn't be very meaningful
+struct Derived1 : public Dummy, public Base
+{
+    Derived1(int x): x_(x) {}
+    virtual int x() const { return x_; }
+    
+  private:
+    int x_;
+};
+
+struct Derived2 : public Dummy, public Base
+{
+    Derived2(int x): x_(x) {}
+    virtual int x() const { return x_; }
+    
+  private:
+    int x_;
+};
+
+static int testUpcast(Base * b)
+{
+    return b->x();
+}
+
+static std::auto_ptr<Base> derived1Factory(int i)
+{
+    return std::auto_ptr<Base>(new Derived1(i));
+}
+
+static std::auto_ptr<Base> derived2Factory(int i)
+{
+    return std::auto_ptr<Base>(new Derived2(i));
+}
+
+static int testDowncast1(Derived1 * d)
+{
+    return d->x();
+}
+
+static int testDowncast2(Derived2 * d)
+{
+    return d->x();
+}
+
 /************************************************************/
 /*                                                          */
 /*                       init the module                    */
@@ -426,6 +488,25 @@ void init_module(py::Module& m)
     over.def(&OverloadTest::p4, "overloaded");
     over.def(&OverloadTest::p5, "overloaded");
     
+    py::ClassWrapper<Base> base(m, "Base");
+    base.def(&Base::x, "x");
+    
+    py::ClassWrapper<Derived1> derived1(m, "Derived1");    
+    // this enables conversions between Base and Derived1
+    // and makes wrapped methods of Base available 
+    derived1.declare_base(base);
+    derived1.def(py::Constructor<int>());
+
+    py::ClassWrapper<Derived2> derived2(m, "Derived2");    
+    // don't enable downcast from Base to Derived2 
+    derived2.declare_base(base, py::without_downcast);
+    derived2.def(py::Constructor<int>());
+    
+    m.def(&testUpcast, "testUpcast");
+    m.def(&derived1Factory, "derived1Factory");
+    m.def(&derived2Factory, "derived2Factory");
+    m.def(&testDowncast1, "testDowncast1");
+    m.def(&testDowncast2, "testDowncast2");
 }
 
 void init_module()
diff --git a/newtypes.h b/newtypes.h
index 94382232..51a27e9d 100644
--- a/newtypes.h
+++ b/newtypes.h
@@ -30,6 +30,8 @@
 
 namespace py {
 
+class InstanceHolderBase;
+
 class TypeObjectBase : public PythonType
 {
  public:
@@ -59,6 +61,11 @@ class TypeObjectBase : public PythonType
     virtual PyObject* instance_getattr(PyObject* instance, const char* name) const;
     virtual int instance_setattr(PyObject* instance, const char* name, PyObject* value) const;
 
+    virtual void * try_class_conversions(InstanceHolderBase*) const { return 0; }
+    virtual void * try_super_class_conversions(InstanceHolderBase*) const { return 0; }
+    virtual void * try_sub_class_conversions(InstanceHolderBase*) const { return 0; }
+    virtual void * convert_from_holder(InstanceHolderBase*) const { return 0; }
+
     // Dealloc is a special case, since every type needs a nonzero tp_dealloc slot.
     virtual void instance_dealloc(PyObject*) const = 0;
 
diff --git a/test_extclass.py b/test_extclass.py
index 138a7107..8a0c06f0 100644
--- a/test_extclass.py
+++ b/test_extclass.py
@@ -130,7 +130,7 @@ But objects not derived from Bar cannot:
     >>> baz.pass_bar(baz)
     Traceback (innermost last):
         ...
-    TypeError: extension class 'Baz' is not derived from 'Bar'.
+    TypeError: extension class 'Baz' is not convertible into 'Bar'.
 
 The clone function on Baz returns a smart pointer; we wrap it into an
 ExtensionInstance and  make it look just like any other Baz instance.
@@ -437,28 +437,28 @@ Testing overloaded free functions
     
 Testing overloaded constructors
 
-    >>> x = OverloadTest()
-    >>> x.getX()
+    >>> over = OverloadTest()
+    >>> over.getX()
     1000
-    >>> x = OverloadTest(1)
-    >>> x.getX()
+    >>> over = OverloadTest(1)
+    >>> over.getX()
     1
-    >>> x = OverloadTest(1,1)
-    >>> x.getX()
+    >>> over = OverloadTest(1,1)
+    >>> over.getX()
     2
-    >>> x = OverloadTest(1,1,1)
-    >>> x.getX()
+    >>> over = OverloadTest(1,1,1)
+    >>> over.getX()
     3
-    >>> x = OverloadTest(1,1,1,1)
-    >>> x.getX()
+    >>> over = OverloadTest(1,1,1,1)
+    >>> over.getX()
     4
-    >>> x = OverloadTest(1,1,1,1,1)
-    >>> x.getX()
+    >>> over = OverloadTest(1,1,1,1,1)
+    >>> over.getX()
     5
-    >>> x = OverloadTest(x)
-    >>> x.getX()
+    >>> over = OverloadTest(over)
+    >>> over.getX()
     5
-    >>> try: x = OverloadTest(1, 'foo')
+    >>> try: over = OverloadTest(1, 'foo')
     ... except TypeError, err:
     ...     assert re.match("No overloaded functions match \(OverloadTest, int, string\)\. Candidates are:",
     ...                     str(err))
@@ -467,25 +467,51 @@ Testing overloaded constructors
     
 Testing overloaded methods
 
-    >>> x.setX(3)
-    >>> x.overloaded()
+    >>> over.setX(3)
+    >>> over.overloaded()
     3
-    >>> x.overloaded(1)
+    >>> over.overloaded(1)
     1
-    >>> x.overloaded(1,1)
+    >>> over.overloaded(1,1)
     2
-    >>> x.overloaded(1,1,1)
+    >>> over.overloaded(1,1,1)
     3
-    >>> x.overloaded(1,1,1,1)
+    >>> over.overloaded(1,1,1,1)
     4
-    >>> x.overloaded(1,1,1,1,1)
+    >>> over.overloaded(1,1,1,1,1)
     5
-    >>> try: x.overloaded(1,'foo')
+    >>> try: over.overloaded(1,'foo')
     ... except TypeError, err:
     ...     assert re.match("No overloaded functions match \(OverloadTest, int, string\)\. Candidates are:",
     ...                     str(err))
     ... else:
     ...     print 'no exception'
+
+Testing base class conversions
+
+    >>> testUpcast(over)
+    Traceback (innermost last):
+    TypeError: extension class 'OverloadTest' is not convertible into 'Base'.
+    >>> der1 = Derived1(333)
+    >>> der1.x()
+    333
+    >>> testUpcast(der1)
+    333
+    >>> der1 = derived1Factory(1000)
+    >>> testDowncast1(der1)
+    1000
+    >>> testDowncast2(der1)
+    Traceback (innermost last):
+    TypeError: extension class 'Base' is not convertible into 'Derived2'.
+    >>> der2 = Derived2(444)
+    >>> der2.x()
+    444
+    >>> testUpcast(der2)
+    444
+    >>> der2 = derived2Factory(1111)
+    >>> testDowncast2(der1)
+    Traceback (innermost last):
+    TypeError: extension class 'Base' is not convertible into 'Derived2'.
 '''
 
 from demo import *