diff --git a/CMakeLists.txt b/CMakeLists.txt
index cb4e65f..5aae9aa 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -63,11 +63,13 @@ endif()
 
 ##-----------------------------------------------------------------------------
 add_library (cruft-vk-icd STATIC
+    icd/fwd.hpp
     ${CMAKE_CURRENT_BINARY_DIR}/icd/vtable.hpp
     ${CMAKE_CURRENT_BINARY_DIR}/icd/dispatch.cpp
     icd/vendor.hpp
     icd/vendor.cpp
     icd/vendor_${VK_LOADER_VENDOR}
+    icd/vtable.cpp
 )
 
 target_link_libraries (cruft-vk-icd cruft-json cruft)
diff --git a/icd/fwd.hpp b/icd/fwd.hpp
new file mode 100644
index 0000000..e69de29
diff --git a/icd/vendor.hpp b/icd/vendor.hpp
index 85bc202..21a857f 100644
--- a/icd/vendor.hpp
+++ b/icd/vendor.hpp
@@ -1,45 +1,46 @@
-#pragma once
-
-#include "vk.hpp"
-
-#include <cruft/util/library.hpp>
-
-#include <string>
-#include <experimental/filesystem>
-
-
-///////////////////////////////////////////////////////////////////////////////
-namespace cruft::vk::icd {
-    struct icd_t {
-        std::string file_format_version;
-        struct {
-            std::experimental::filesystem::path library_path;
-            std::string api_version;
-        } icd;
-    };
-
-
-    std::vector<icd_t>
-    enumerate (void);
-
-
-    class vendor {
-    public:
-        vendor (icd_t const&);
-        vendor (::cruft::library &&);
-
-        struct vtable_t {
-            VkResult (*CreateInstance) (
-                VkInstanceCreateInfo const*,
-                VkAllocationCallbacks const*,
-                VkInstance*
-            ) noexcept;
-        } vtable;
-
-    private:
-        using get_proc_t = void* (*)(VkInstance, char const*);
-
-        ::cruft::library m_library;
-        get_proc_t const m_get_proc;
-    };
-}
\ No newline at end of file
+#pragma once
+
+#include "vk.hpp"
+
+#include <cruft/util/library.hpp>
+
+#include <string>
+#include <experimental/filesystem>
+
+
+///////////////////////////////////////////////////////////////////////////////
+namespace cruft::vk::icd {
+    struct icd_t {
+        std::string file_format_version;
+        struct {
+            std::experimental::filesystem::path library_path;
+            std::string api_version;
+        } icd;
+    };
+
+
+    std::vector<icd_t>
+    enumerate (void);
+
+
+    class vendor {
+    public:
+        vendor (icd_t const&);
+        vendor (::cruft::library &&);
+
+        struct vtable_t {
+            VkResult (*CreateInstance) (
+                VkInstanceCreateInfo const*,
+                VkAllocationCallbacks const*,
+                VkInstance*
+            ) noexcept;
+        } vtable;
+
+    private:
+        ::cruft::library m_library;
+
+    public:
+        using get_proc_t = void* (*)(VkInstance, char const*);
+        get_proc_t const m_get_proc;
+    };
+}
diff --git a/icd/vtable.cpp b/icd/vtable.cpp
new file mode 100644
index 0000000..054bc77
--- /dev/null
+++ b/icd/vtable.cpp
@@ -0,0 +1,14 @@
+#include "icd/vtable.hpp"
+
+#include "vendor.hpp"
+
+using cruft::vk::icd::instance_table;
+
+instance_table::instance_table (vendor &src)
+{
+#define LOADFN(name) this->name = reinterpret_cast<decltype(this->name)> (src.m_get_proc(
+
+    this->vkCreateInstance = reinterpret_cast<decltype(this->vkCreateInstance)> (
+        src.m_get_proc(nullptr, "vkCreateInstance")
+    );
+}
diff --git a/tools/info.cpp b/tools/info.cpp
index 9c011fa..04992e2 100644
--- a/tools/info.cpp
+++ b/tools/info.cpp
@@ -4,7 +4,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  *
  * Copyright:
- *      2017, Danny Robson <danny@nerdcruft.net>
+ *      2017-2018, Danny Robson <danny@nerdcruft.net>
  */
 
 #include <cruft/util/iterator.hpp>
@@ -17,6 +17,7 @@
 
 
 #include "../icd/vendor.hpp"
+#include "icd/vtable.hpp"
 
 
 ///////////////////////////////////////////////////////////////////////////////
@@ -25,6 +26,7 @@ main (int, char**)
 {
     for (auto const &i: cruft::vk::icd::enumerate ()) {
         cruft::vk::icd::vendor v (i);
+        cruft::vk::icd::instance_table t (v);
 
         //std::cout << "available_layers: [ "
         //    << cruft::make_infix (cruft::vk::instance::available_layers ())
diff --git a/tools/spec.py b/tools/spec.py
index e5c2e7a..dce02ab 100644
--- a/tools/spec.py
+++ b/tools/spec.py
@@ -229,6 +229,7 @@ class handle(type):
 
         super().__init__(name, depends=[type])
         self.type = type
+        self.parent = node.attrib.get('parent', None)
 
     def declare(self):
         return "struct %(name)s_t; using %(name)s = %(name)s_t*;" % {
@@ -236,6 +237,20 @@ class handle(type):
             "type": self.type
         }
 
+    def has_parent(self, name:str, reg:registry) -> bool:
+        """
+        Recursively check if this type is derived from a given parent type.
+        """
+        assert name
+        assert reg
+
+        if not self.parent:
+            return False
+        if self.parent == name:
+            return True
+
+        return reg.types[self.parent].has_parent(name, reg)
+
 
 class enum(type):
     def __init__(self,node):
@@ -395,10 +410,14 @@ class command(type):
                 **kwargs
             )
 
-            self.type = ""
+            self.type = node.find('type').text
+
+            self.param = ""
             for i in node.iter():
-                self.type += i.text or ""
-                self.type += i.tail or ""
+                self.param += i.text or ""
+                self.param += i.tail or ""
+            # normalise whitespace
+            self.param = " ".join(self.param.split())
 
     def __init__(self, node):
         assert node.tag == "command"
@@ -416,9 +435,43 @@ class command(type):
         return "%(result)s %(name)s (%(params)s) noexcept;" % {
             'name': rename(self.name),
             'result': self.result,
-            'params': ", ".join(p.type for p in self.params)
+            'params': ", ".join(p.param for p in self.params)
         }
 
+    def is_instance(self, reg:registry):
+        assert reg
+
+        if not self.params:
+            return True
+
+        first_arg = self.params[0].type
+        if first_arg == 'VkInstance':
+            return True
+
+        first_obj = reg.types[first_arg]
+
+        # If the first type isn't a handle of any description then it should
+        # be an instance function.
+        if not isinstance(first_obj, handle):
+            return True
+
+        # Both VkInstance and VkPhysicalDevice are listed as possible instance
+        # parameters.
+        #
+        # Test that the handle is derived from VkInstance, and not derived from
+        # VkDevice. The second test is required because VkDevice is indirectly
+        # derived from VkInstance. This approach buys us a little more
+        # generality.
+
+        if not first_obj.has_parent('VkInstance', reg):
+            return False
+        if first_arg == 'VkDevice' or first_obj.has_parent('VkDevice', reg):
+            return False
+        return True
+
+    def is_device(self, reg:registry):
+        return not self.is_instance(reg)
+
 
 class require(object):
     def __init__(self, root):
@@ -586,7 +639,7 @@ def parse_types(reg:registry, root):
             ]
 
             if category in supported_categories:
-                obj = globals()[category] (t)
+                obj = globals()[category](t)
                 reg.types[name] = obj
             else:
                 raise 'unhandled type'
@@ -729,17 +782,43 @@ if __name__ == '__main__':
         dst.write('}\n')
 
     with open(args.icd, 'w') as icd:
-        icd.write("""
+        commands = [i for i in q if isinstance(i, command)]
+        instance_commands = [i for i in commands if i.is_instance(reg)]
+        device_commands = [i for i in commands if i.is_device(reg)]
+
+        assert len(instance_commands) + len(device_commands) == len(commands)
+
+        icd.write(f"""
         #include "vk.hpp"
 
-        namespace cruft::vk::icd {
-        struct vtable {
+        #include <cruft/util/preprocessor.hpp>
+
+        #define MAP_COMMANDS(FUNC) MAP0(FUNC,{",".join(i.name for i in commands)})
+        #define MAP_INSTANCE_COMMANDS(FUNC) MAP0(FUNC,{",".join(i.name for i in instance_commands)})
+        #define MAP_DEVICE_COMMANDS(FUNC) MAP0(FUNC,{",".join(i.name for i in device_commands)})
+
+        namespace cruft::vk::icd {{
+        struct vendor;
+
+        struct func {{
+            void *handle;
+            void const *table;
+        }};
+
+        struct instance_table {{
+            instance_table (vendor &);
         """)
 
-        for obj in q:
-            if not isinstance(obj, command):
-                continue
-            icd.write(f"{obj.result} (*{obj.name}) ({','.join(p.type for p in obj.params)});\n")
+        for obj in instance_commands:
+            icd.write(f"{obj.result} (*{obj.name}) ({','.join(p.param for p in obj.params)}) = nullptr;\n")
+
+        icd.write("""};
+
+        struct device_table {
+        """)
+
+        for obj in device_commands:
+            icd.write(f"{obj.result} (*{obj.name}) ({','.join(p.param for p in obj.params)}) = nullptr;\n")
 
         icd.write("""
         };
@@ -756,16 +835,25 @@ if __name__ == '__main__':
 
         #pragma GCC diagnostic ignored "-Wunused-parameter"
 
-        static cruft::vk::icd::vtable *s_vtable = nullptr;
+        static cruft::vk::icd::instance_table const *i_table = nullptr;
+        static cruft::vk::icd::device_table const *d_table = nullptr;
         """)
 
-
-        for obj in q:
-            if not isinstance(obj, command):
-                continue
+        for obj in commands:
+            if obj.is_instance(reg):
+                table = "i_table"
+            elif obj.is_device(reg):
+                table = "d_table"
+            else:
+                raise Exception("unhandled command type")
 
             dispatch.write(f"""
-            extern "C" {obj.result} {rename(obj.name)} ({", ".join(p.type for p in obj.params)}) noexcept {{
-                return (*s_vtable->{obj.name})({", ".join(p.name for p in obj.params)});
-            }}
+            extern "C" {obj.result} {rename(obj.name)} ({", ".join(p.param for p in obj.params)}) noexcept {{
+                auto const entry = reinterpret_cast<cruft::vk::icd::func const*> ({obj.params[0].name});
+                auto const *table = reinterpret_cast<decltype({table})> (entry->table);
+
+                return (table->{obj.name})(
+                    reinterpret_cast<decltype({obj.params[0].name})> (entry->handle),
+                    {", ".join(p.name for p in obj.params[1:])}
+                );
             """)